Flexible battery and electronic device

ABSTRACT

To provide a lithium-ion storage battery or electronic device that is flexible and highly safe. One embodiment of the present invention is a flexible storage battery including a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, an exterior body that surrounds the positive electrode, the negative electrode, and the separator, and a wiring provided along the exterior body. At least part of the wiring is more easily breakable by deformation than the exterior body. The wiring is more vulnerable to deformation than the exterior body and thus damaged earlier than the exterior body. Damage to the wiring is detected and an alert is sent to a user; thus, the use of the storage battery can be stopped before the exterior body is damaged.

BACKGROUND OF THE INVENTION 1. Field of the Invention

Embodiments of the present invention relate to a flexible storagebattery and a flexible electronic device.

Note that one embodiment of the present invention is not limited to theabove technical field. The technical field of one embodiment of theinvention disclosed in this specification and the like relates to anobject, a method, or a manufacturing method. One embodiment of thepresent invention relates to a process, a machine, manufacture, or acomposition of matter. Specifically, examples of the technical field ofone embodiment of the present invention disclosed in this specificationinclude a semiconductor device, a display device, a liquid crystaldisplay device, a light-emitting device, a lighting device, a storagebattery, a storage device, a method for driving any of them, and amethod for manufacturing any of them.

2. Description of the Related Art

In recent years, a variety of storage batteries such as lithium-ionstorage batteries, lithium-ion capacitors, air cells, and fuel cellshave been actively developed. In particular, demand for lithium-ionstorage batteries with high output and high energy density has rapidlygrown with the development of the semiconductor industry and with thegrowth of demand for energy saving, for electronic devices, for example,portable information terminals such as mobile phones, smartphones, andlaptop computers, portable music players, and digital cameras; medicalequipment; next-generation clean energy vehicles such as hybrid electricvehicles (HEVs), electric vehicles (EVs), and plug-in hybrid electricvehicles (PHEVs); stationary storage batteries; and the like. Thelithium-ion storage batteries are essential for today's society.Furthermore, with the growing expectations for flexible devices orwearable devices in recent years, the development of lithium-ion storagebatteries that have flexibility to be changed in form in accordance witha change in the form of the devices, i.e., flexible storage batteries isurgently necessary and has partly been started (Patent Document 1).

A lithium-ion storage battery, which is a nonaqueous secondary battery,includes a positive electrode, a negative electrode, a separator, anonaqueous electrolytic solution, and an exterior body covering thesecomponents. In lithium-ion storage batteries, positive electrodes andnegative electrodes are generally used; the positive electrodes eachinclude a positive electrode current collector made of a metal such asaluminum and a positive electrode mix that includes a positive electrodeactive material capable of receiving and releasing lithium ions and thatis applied to each surface of the positive electrode current collector,and the negative electrodes each include a negative electrode currentcollector made of copper or the like and a negative electrode mix thatincludes a negative electrode active material capable of receiving andreleasing lithium ions and that is applied to each surface of thenegative electrode current collector. These positive and negativeelectrodes are insulated from each other by a separator providedtherebetween, and the positive electrode and the negative electrode areelectrically connected to a positive electrode terminal and a negativeelectrode terminal, respectively, which are provided on the exteriorbody. The exterior body has a certain shape such as a cylindrical shapeor a rectangular shape.

REFERENCES Patent Document

[Patent Document 1] Japanese Published Patent Application No.2008-146917

SUMMARY OF THE INVENTION

As the number of times a flexible lithium-ion storage battery is changedin form increases, fatigue of (damage to) an exterior body thereofholding components and an electrolytic solution of the batteryaccumulates. Accumulation of fatigue (damage) might break the exteriorbody or a sealed structure, resulting in entry of air into the storagebattery. Furthermore, fatigue might build at a tab electrode (terminalportion) of each of a positive electrode and a negative electrode of thestorage battery, which breaks the terminal portion and cause failure ofthe storage battery in some cases.

When the lithium-ion storage battery is broken and air enters therein,the components in the storage battery might react with air or moisture,generate heat, and catch fire, leading to a critical accident such asexplosion. Even if a mechanism that detects a breakage of the exteriorbody or the like and sends an alert is introduced to prevent such acritical accident, it is difficult to preclude the accident after theexterior body or the like is broken.

For this reason, a storage battery that can send an alert to a userbefore fatigue of (damage to) its component accumulates to causebreakage is needed.

In view of the above, an object of one embodiment of the presentinvention is to provide a flexible storage battery that has a functionof sending an alert to a user before its component is damaged because offatigue (damage). Another object is to ensure the safety of a flexiblestorage battery.

Another object of one embodiment of the present invention is to providea lithium-ion storage battery or electronic device that is flexible andhighly safe. Another object of one embodiment of the present inventionis to provide a novel lithium-ion storage battery, a novel electronicdevice, or the like.

Note that the descriptions of these objects do not disturb the existenceof other objects. In one embodiment of the present invention, there isno need to achieve all the objects. Other objects will be apparent fromand can be derived from the descriptions of the specification, thedrawings, the claims, and the like.

One embodiment of the present invention is a flexible storage batteryincluding a positive electrode, a negative electrode, a separatorbetween the positive electrode and the negative electrode, an exteriorbody that surrounds the positive electrode, the negative electrode, andthe separator, and a wiring provided along the exterior body. At leastpart of the wiring is more easily breakable by deformation than theexterior body.

One embodiment of the present invention is a flexible storage batteryincluding a positive electrode, a negative electrode, a tab electrode, awiring, a separator between the positive electrode and the negativeelectrode, and an exterior body that surrounds the positive electrode,the negative electrode, and the separator. The tab electrode isconnected to one of the positive electrode and the negative electrode.The wiring is provided along the tab electrode. At least part of thewiring is more easily breakable by deformation than the tab electrode.

Note that in the flexible storage battery of one embodiment of thepresent invention, the wiring may be electrically connected to a firstcircuit configured to detect damage to the wiring. Furthermore, theflexible storage battery may include the first circuit. Furthermore, inthe flexible storage battery, the first circuit may be configured tooutput a signal when the first circuit detects damage to the wiring; thesignal is different from a signal output when the first circuit detectsno damage to the wiring

There may be provided a flexible electronic device including the storagebattery of one embodiment of the present invention, a display portion,and the first circuit. The first circuit is electrically connected tothe wiring. The first circuit is configured to detect damage to thewiring. Alternatively, there may be provided a flexible electronicdevice including the storage battery of one embodiment of the presentinvention, a display portion, and the first circuit. The first circuitis electrically connected to the wiring. The first circuit is configuredto detect damage to the wiring. The display portion is configured todisplay an image when the first circuit detects damage to the wiring;the image is different from an image displayed when the first circuitdetects no damage to the wiring.

In one embodiment of the present invention, a wiring that is more easilybreakable than a component that is to get fatigued (to be damaged) isprovided along the component so that the wiring is changed in form inaccordance with a change in the form of the component. Thus, not onlythe component but also the wiring becomes fatigued (is damaged) bydeformation. Fatigue (damage to) accumulated in the component is similarto that accumulated in the wiring; however, the wiring is damagedearlier than the component since the wiring is more easily breakablethan the component.

Thus, a circuit connected to the wiring is configured to detect damageto the wiring. In this case, when the circuit detects damage to thewiring due to fatigue (damage), the use of a storage battery or anelectronic device can be stopped. Here, the component in contact withthe wiring is also correspondingly fatigued (damaged); however, it ispossible to prevent the situation where the component is furtherfatigued and damaged by the further use of the storage battery orelectronic device and an accident is caused.

One embodiment of the present invention can provide a flexible storagebattery that is configured to send an alert to a user before itscomponent is damaged because of fatigue (damage). Alternatively, oneembodiment of the present invention can ensure the safety of a flexiblestorage battery.

Alternatively, one embodiment of the present invention can provide alithium-ion storage battery or electronic device that is flexible andhighly safe. Alternatively, one embodiment of the present invention canprovide a novel lithium-ion storage battery, a novel electronic device,or the like.

Note that the description of these effects does not disturb theexistence of other effects. One embodiment of the present invention docsnot have to have all the effects listed above. Other effects will beapparent from and can be derived from the description of thespecification, the drawings, the claims, and fee like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate a lithium-ion storage battery of oneembodiment of the present invention.

FIGS. 2A to 2D illustrate the radius of curvature.

FIGS. 3A to 3C illustrate the radius of curvature.

FIGS. 4A to 4C illustrate a coin-type storage battery.

FIGS. 5A and 5B illustrate a cylindrical storage battery.

FIGS. 6A and 6B illustrate a laminated storage battery.

FIG. 7 illustrates an appearance of a storage battery.

FIG. 8 illustrates an appearance of a storage battery.

FIGS. 9A to 9C illustrate a method for fabricating a storage battery.

FIGS. 10A to 10E illustrate flexible laminated storage batteries.

FIGS. 11A and 11B illustrate an example of a storage battery.

FIGS. 12A1, 12A2, 12B1, and 12B2 each illustrate an example of a storagebattery.

FIGS. 13A and 13B each illustrate an example of a storage battery.

FIGS. 14A and 14B each illustrate an example of a storage battery.

FIG. 15 illustrates an example of a storage battery.

FIGS. 16A and 16B each illustrate an application mode of a storagebattery

FIG. 17 is a block diagram illustrating one embodiment of the presentinvention.

FIGS. 18A, 18B, and 18C are schematic views each illustrating oneembodiment of the present invention.

FIG. 19 is a circuit diagram illustrating one embodiment of the presentinvention.

FIG. 20 is a circuit diagram illustrating one embodiment of the presentinvention.

FIGS. 21A to 21C are schematic views each illustrating one embodiment ofthe present invention.

FIG. 22 is a block diagram illustrating one embodiment of the presentinvention.

FIG. 23 is a flow chart showing one embodiment of the present invention.

FIGS. 24A and 24B illustrate an appearance and a cross-sectionalstructure of a storage battery of one embodiment of the presentinvention.

FIGS. 25A and 25B are circuit diagrams each illustrating one embodimentof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described below in detailwith reference to the drawings. However, the present invention is notlimited to the description below, and it is easily understood by thoseskilled in the art that modes and details disclosed herein can bemodified in various ways. Further, the present invention is notconstrued as being limited to the description of the embodiments.

Note that in drawings explained in this specification, the sizes,thicknesses, or the like of components such as a positive electrode, anegative electrode, an active material layer, a separator, and anexterior body are exaggerated for simplicity of explanation in somecases. Therefore, the sizes of the components are not limited to thesizes in the drawings and relative sizes between the components.

Note that the ordinal numbers such as “first”, “second”, “third” in thisspecification and the like are used for convenience and do not denotethe order of steps, the positional relation, or the like. Therefore, forexample, description can be made even when “first” is replaced with“second” or “third”, as appropriate. In addition, the ordinal numbers inthis specification and the like are not necessarily the same as thosewhich specify one embodiment of the present invention.

Note that in structures of the present invention described in thisspecification and the like, the same portions or portions having similarfunctions are denoted by common reference numerals in differentdrawings, and descriptions thereof are not repeated. Further, the samehatching pattern is applied to portions having similar functions, andthe portions are not especially denoted by reference numerals in somecases.

In this specification, flexibility refers to a property of an objectbeing flexible and bendable. In other words, it is a property of anobject that can be changed in form in response to an external forceapplied to the object, and elasticity or restorability to the formershape is not taken into consideration. A flexible storage battery can bechanged in form in response to an external force. A flexible storagebattery can be used with its shape fixed in a state of being changed inform, can be used while repeatedly changed in form, and can be used in astate of not changed in form.

The descriptions in embodiments of fee present invention can be combinedwith each other as appropriate.

Embodiment 1

In this embodiment, a lithium-ion storage battery of one embodiment ofthe present invention will be described.

A method for fabricating a lithium-ion storage battery 110 of oneembodiment of the present invention will be described below using FIGS.1A and 1B. FIG. 1B is a cross-sectional view of the lithium-ion storagebattery 110. In the schematic cross-sectional view, a positive electrodecurrent collector 100, a positive electrode active material layer 101, aseparator 104, a negative electrode active material layer 103, and anegative electrode current collector 102 are stacked and enclosedtogether with an electrolytic solution 105 by an exterior body 207. Notethat the active material layers can be formed on both surfaces of thecurrent collector, and the storage battery can have a layered structure.Furthermore, in this embodiment, wirings 206 are provided along theexterior body 207, for example. In addition, a circuit 208 connected tothe wirings 206 is provided over the exterior body 207, for example.

<<Wiring and Circuit>>

The wirings 206 included in the flexible lithium-ion storage battery 110of one embodiment of the present invention and the circuit 208 having afunction of detecting damage to the wirings 206 will be described.

The wirings 206 are provided to protect a component to be protected frombeing damaged by being deformed. Thus, the wirings 206 are formed usinga material that is less resistant to fatigue due to deformation and morelikely to be damaged (e.g., fractured) than the component. The wirings206 are provided along the component so as to be changed in form whenfee component is changed in form.

In this embodiment, the wirings 206 are provided along the exterior bodyto protect the exterior body from being damaged because of deformation,for example. When the lithium-ion storage battery 110 provided with thewiring 206 is changed in form, components included in the lithium-ionstorage battery 110 are changed in form, so that the component to beprotected also gets fatigued (is also damaged). Not only the componentto be protected but the wirings 206 become fatigued (is damaged) bydeformation. Therefore, similar fatigue (damage) accumulates in thecomponent and the wirings 206.

Here, since the wirings 206 are less resistant to fatigue (damage) dueto deformation than the component to be protected, they are damaged(e.g., fractured) earlier than the component when fatigue of the wirings206 builds and reaches the limit. The physical properties of the damagedwirings 206 are changed; for example, the conductivity and thermalconductivity thereof are reduced.

In view of the above, in one embodiment of the present invention, thecircuit 208 having a function of detecting a change in the physicalproperty (e.g., a reduction in conductivity) of the wirings 206 due todamage is connected to the wirings 206. Thus, when the circuit 208detects damage to the wirings 206 due to fatigue, it can sendinformation that damage to the wirings 206 is detected to an electronicdevice including the lithium-ion storage battery 110 through a tabelectrode 516, so that a user of the electronic device can be notifiedof the information. The user who has received the notice can turn offthe electronic device at the convenient timing. The component to beprotected that is in contact with the wirings 206 is alsocorrespondingly fatigued (damaged); thus, the lithium-ion storagebattery 110 can be replaced with a new storage battery before thecomponent is further fatigued and damaged by the further use of thelithium-ion storage battery 110 or the electronic device, and anaccident is caused.

The circuit 208 does not necessarily notify the electronic device of theinformation when detecting damage to the wirings 206; in that case, amechanism may be provided which automatically stops discharge or chargeof the lithium-ion storage battery 110 with a control unit (notillustrated) that detects overdischarge, overcharge, or overcurrent ofthe storage battery and that is connected to the circuit 208, whendamage to the wirings 206 is detected.

In either case, one embodiment of the present invention can stop the useof the lithium-ion storage battery 110 before the component thereof isdamaged; accordingly, an accident can be precluded.

Here, the wirings 206 can be formed using a material that is more easilybreakable than the component to be protected from being broken byfatigue (damage) due to deformation. Thus, any of a variety of materialscan be used for the wirings 206 in accordance with the property of thecomponent. Note that in this specification, the property of being easilybroken or fractured by accumulation of fatigue (damage) due todeformation may be expressed by the term such as “vulnerable”, “easilybreakable”, “having a low fatigue limit”, “easily breakable by fatigue(damage) due to deformation”, or “easily breakable by deformation”.

An S-N curve is broadly used to express how many times of repeatedstress application a material can resist or how many times of stressapplication and how much stress breaks the material. In general, theresistance to fatigue of a material is measured by a fatigue test (JIS:JISZ2273) of the material, and stress applied to the material in thetest has an amplitude of a sine wave that is time-dependent. Such an S-Ncurve is obtained by plotting fatigue test results when the verticalaxis represents stress amplitude and the horizontal axis represents thenumber of times N stress application is repeated until fracture.

In one embodiment of the present invention, the wirings 206 can beformed using a material that has an S-N curve closer to the horizontalaxis than the S-N curve of the component to be protected from beingbroken by fatigue (damage) due to deformation. However, a material ofthe wirings 206 is not limited to this.

In some cases, it is difficult to take out the wirings 206 and thecomponent to be protected from being broken by fatigue (damage) due todeformation from the lithium-ion storage battery 110 of one embodimentof the present invention and measure the resistance to fatigue (damage)due to deformation thereof. In one embodiment of the present invention,the lithium-ion storage battery 110 is repeatedly subjected to a bendtest, and if the wirings 206 are broken or damaged (e.g., fractured)earlier than the component, the wirings 206 can be determined to be morevulnerable to fatigue (damage) due to deformation than the component.

Next, the circuit 208 that detects damage to the wirings 206 may beprovided either in the control unit that detects overdischarge,overcharge, or overcurrent or separately from the control unit.Depending on the kind of the component to be protected from being brokenby fatigue (damage) due to deformation, the circuit 208 can be includedin a unit or circuit that has any other function. Note that an exampleof the configuration of the circuit 208 and an example of the operationsthereof will be described later.

<<Structure of Positive Electrode>>

The positive electrode will be described. The positive electrodeincludes the positive electrode active material layer 101 and thepositive electrode current collector 100.

As a material for a positive electrode active material used for thepositive electrode active material layer 101, a material into and fromwhich carrier ions such as lithium ions can be inserted and extractedcan be used. Examples of the material are a lithium-containing materialwith an olivine crystal structure, a layered rock-salt crystalstructure, or a spinel crystal structure, and the like.

Typical examples of a lithium-containing material with an olivinecrystal structure (LiMPO₄ (general formula) (M is Fe(II), Mn(II),Co(II), or Ni(II))) are LiFePO₄, LiNiPO₄, LiCoPO₄, LiMnPO₄,LiFe_(a)Ni_(b)PO₄, LiFe_(a)Co_(b)PO₄, LiFe_(a)Mn_(b)PO₄,LiNi_(a)Co_(b)PO₄, LiNi_(a)Mn_(b)PO₄ (a+b≤1, 0<a<1, and 0<b<1),LiFe_(c)Ni_(d)Co_(e)PO₄, LiFe_(c)Ni_(d)Mn_(e)PO₄,LiNi_(c)Co_(d)Mn_(e)PO₄ (c+d+e≤1, 0<c<1, 0<d<1, and 0<e<1), andLiFe_(f)Ni_(g)Co_(h)Mn_(i)PO₄ (f+g+h+i≤1, 0<f<1, 0<g<1, 0<h<1, and0<i<1).

For example, lithium iron phosphate (LiFePO₄) is preferable because itproperly has properties necessary for the positive electrode activematerial, such as safety, stability, high capacity density, highpotential, and the existence of lithium ions which can be extracted ininitial oxidation (charge).

Examples of a lithium-containing material with a layered rock-saltcrystal structure include lithium cobalt oxide (LiCoO₂), LiNiO₂, LiMnO₂,Li₂MnO₃, a NiCo-containing material (general formula: LiNi_(x)Co_(1−x)O₂(0<x<1)) such as LiNi_(0.8)Co_(0.2)O₂, a NiMn-containing material(general formula: LiNi_(x)Mn_(1−x)O₂ (0<x<1)) such asLiNi_(0.5)Mn_(0.5)O₂, a NiMnCo-containing material (also referred to asNMC) (general formula: LiNi_(x)Mn_(y)Co_(1−x−y)O₂ (x>0, y>0, x+y<1))such as LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂. Moreover,Li(Ni_(0.8)Co_(0.15)Al_(0.05))O₂, Li₂MnO₃-LiMO₂ (M=Co, Ni, or Mn), andthe like can be given as the examples.

In particular, LiCoO₂ is preferable because it has advantages such ashigh capacity, higher stability in the air than that of LiNiO₂, andhigher thermal stability than that of LiNiO₂.

Examples of a lithium-containing material with a spinel crystalstructure include LiMn₂O₄, Li_(1+x)Mn_(2−x)O₄, Li(MnAl)₂O₄, andLiMn_(1.5)Ni_(0.5)O₄.

It is preferred that a small amount of lithium nickel oxide (LiNiO₂ orLiNi_(1−x)MO₂ (M=Co, Al, or the like)) be added to a lithium-containingmaterial with a spinel crystal structure that contains manganese, suchas LiMn₂O₄, in which case advantages such as inhibition of thedissolution of manganese and the decomposition of an electrolyticsolution can be obtained.

Alternatively, a composite oxide expressed by Li_((2−j))MSiO₄ (generalformula) (M is Fe(II), Mn(II), Co(II), or Ni(II); 0≤j≤2) may be used asthe positive electrode active material. Typical examples of the generalformula Li_((2−j))MSiO₄ are Li_((2−j))FeSiO₄, Li_((2−j))NiSiO₄,Li_((2−j))CoSiO₄, Li_((2−j))MnSiO₄, Li_((2−j))Fe_(k)Ni_(l)SiO₄,Li_((2−j))Fe_(k)Co_(l)SiO₄, Li_((2−j))Fe_(k)Mn_(l)SiO₄,Li_((2−j))Ni_(k)Co_(l)SiO₄, Li_((2−f))Ni_(k)Mn_(l)SiO₄ (k+l≤1, 0<k<1,and 0<l<1), Li_((2−j))Fe_(m)Ni_(n)Co_(q)SiO₄,Li_((2−j))Fe_(m)Ni_(n)Mn_(q)SiO₄, Li_((2−j))Ni_(m)Co_(n)Mn_(q)SiO₄(m+n+q≤1, 0<m<1, 0<n<1, and 0<q<1), andLi_((2−j))Fe_(r)Nih_(s)Co_(t)Mn_(u)SiO₄ (r+s+t+u≤1, 0<r<1, 0<s<1, 0<r<1,and 0<u<1).

Still alternatively, a nasicon compound expressed by A_(x)M₂(XO₄)₃(general formula) (A=Li, Na, or Mg, M=Fe, Mn, Ti, V, Nb, or Al, X=S, P,Mo, W, As, or Si) can be used for the positive electrode activematerial. Examples of the nasicon compound are Fe₂(MnO₄)₃, Fe₂(SO₄)₃,and Li₃Fe₂(PO₄)₃. Further alternatively, for example, a compoundexpressed by Li₂MPO₄F, Li₂MP₂O₇, or Li₃MO₄ (general formula) (M=Fe orMn), a pcrovslritc fluoride such as NaF₃ and FeF₃, a metal chalcogenide(a sulfide, a selenide, or a telluride) such as TiS₂ and MoS₂, alithium-containing material with an inverse spinel structure such asLiMVO₄, a vanadium oxide (V₂O₅, V₆O₁₃, LiV₃O₈, or the like), a manganeseoxide, or an organic sulfur compound can be used as the positiveelectrode active material.

In the case where carrier ions are alkali metal ions other than lithiumions, or alkaline-earth metal ions, a material containing an alkalimetal (e.g., sodium and potassium) or an alkaline-earth metal (e.g.,calcium, strontium, barium, beryllium, and magnesium) instead of lithiumin any of the above compounds and oxides may be used as the positiveelectrode active material. For example, the positive electrode activematerial may be a sodium-containing layered oxide such as NaFeO₂ orNa_(2/3)[Fe_(1/2)Mn_(1/2)]O₂.

Further alternatively, any of the aforementioned materials may becombined to be used as the positive electrode active material. Forexample, a solid solution obtained by combining two or more of the abovematerials can be used as the positive electrode active material. Forexample, a solid solution of LiCo_(1/3)Mn_(1/3)Ni_(1/3)O₂ and Li₂MnO₃can be used as the positive electrode active material.

The average diameter of primary particles of the positive electrodeactive material is preferably greater than or equal to 50 nm and lessthan or equal to 100 μm.

The positive electrode active material and a negative electrode activematerial have a main role in battery reactions of the storage battery,and receive and release carrier ions. To increase the lifetime of thestorage battery, a material that has a small amount of capacity relatingto irreversible battery reactions and has high charge and dischargeefficiency is preferably used for the active materials.

The active material is in contact with an electrolytic solution. Whenthe active material reacts with the electrolytic solution, the activematerial is lost and deteriorates by the reaction, which decreases thecapacity of the storage battery. Therefore, it is preferable that such areaction not be caused in the storage battery so that the storagebattery hardly deteriorates.

Examples of the conductive additive of the electrode include acetyleneblack (AB), graphite (black lead) particles, carbon nanotubes, graphene,and fullerene.

A network for electrical conduction can be formed in the electrode bythe conductive additive. The conductive additive also allows themaintenance of a path for electric conduction between the positiveelectrode active material particles. The addition of the conductiveadditive to the positive electrode active material layer 101 increasesthe electrical conductivity of the positive electrode active materiallayer 101.

As the binder, polyvinylidene fluoride (PVDF) as a typical example,polyimide, polytetrafluoroethylene, polyvinyl chloride,ethylene-propylene-diene polymer, fluorine rubber, polymethylmethacrylate, polyethylene, nitrocellulose, or the like can be used.

The binder content in the positive electrode active material layer 101is preferably greater than or equal to 1 wt % and less than or equal to10 wt %. more preferably greater than or equal to 2 wt % and less thanor equal to 8 wt %, still more preferably greater than or equal to 3 wt% and less titan or equal to 5 wt %. The conductive additive content inthe positive electrode active material layer 101 is preferably greaterthan or equal to 1 wt % and less than or equal to 10 wt %, morepreferably greater than or equal to 1 wt % and less than or equal to 5wt %.

In the case where the positive electrode active material layer 101 isformed by a coating method, the positive electrode active material, thebinder, the conductive additive, and a dispersion medium are mixed toform an electrode slurry, and the electrode slurry is applied to thepositive electrode current collector 100 and dried.

The positive electrode current collector 100 can be formed using amaterial which has high conductivity and is not alloyed with a carrierion of lithium or the like, such as stainless steel, gold, platinum,aluminum, and titanium, an alloy thereof, and the like. Alternatively,an aluminum alloy to which an element that improves heat resistance,such as silicon, titanium, neodymium, scandium, and molybdenum, is addedcan be used. Still alternatively, a metal element which forms silicideby reacting with silicon can be used. Examples of the metal elementwhich forms silicide by reacting with silicon include zirconium,titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum,tungsten, cobalt, nickel, and the like. The positive electrode currentcollector 100 can have a foil-like shape, a plate-like shape (sheet-likeshape), a net-like shape, a punching-metal shape, an expanded-metalshape, or the like as appropriate.

Through the above steps, the positive electrode of the lithium-ionstorage battery can be formed.

<<Structure of Negative Electrode>>

Next, the negative electrode will be described with reference to FIG.1A. The negative electrode includes the negative electrode activematerial layer 103 and the negative electrode current collector 102.Steps of forming the negative electrode will be described below.

Examples of the carbon-based material as a negative electrode activematerial used for the negative electrode active material layer 103include graphite, graphitizing carbon (soft carbon), non-graphitizingcarbon (hard carbon), a carbon nanotube, graphene, carbon black, and thelike. Examples of the graphite include artificial graphite such asmeso-carbon microbeads (MCMB), coke-based artificial graphite, orpitch-based artificial graphite and natural graphite such as sphericalnatural graphite. In addition, examples of the shape of the graphiteinclude a flaky shape and a spherical shape.

Other than the carbon-based material, a material that enablescharge-discharge reactions by an alloying reaction and a dealloyingreaction with lithium can be used for the negative electrode activematerial. A material containing at least one of Ga, Si, Al, Ge, Sn, Pb,Sb, Bi, Ag, Zn, Cd, In, and the like can be used, for example. Suchelements have a higher capacity than carbon. In particular, silicon hasa high theoretical capacity of 4200 mAh/g. Examples of the alloy-basedmaterial using such elements include Mg₂Si, Mg₂Ge, Mg₂Sn, SnS₂, V₂Sn₃,FeSn₂, CoSn₂, Ni₃Sn₂, Cu₆Sn₅, Ag₃Sn, Ag₃Sb, Ni₂MnSb, CeSb₃, LaSn₃,La₃Co₂Sn₇, CoSb₃, InSb, SbSn, and the like.

Alternatively, for the negative electrode active material, an oxide suchas SiO, SnO, SnO₂, titanium dioxide (TiO₂), lithium titanium oxide(Li₄Ti₅O₁₂), lithium-graphite intercalation compound (Li_(x)C₆), niobiumpentoxide (Nb₂O₅), tungsten oxide (WO₂), or molybdenum oxide (MoO₂) canbe used.

Still alternatively, for the negative electrode active material,Li_(3−x)M_(x)N (M=Co, Ni, or Cu) with a Li₃N structure, which is anitride containing lithium and a transition metal, can be used. Forexample, Li_(2.6)Co_(0.4)N₃ is preferable because of high charge anddischarge capacity (900 mAh/g and 1890 mAh/cm₃).

When a nitride containing lithium and a transition metal is used,lithium ions are contained in the negative electrode active material andthus the negative electrode active material can be used in combinationwith a material for a positive electrode active material that does notcontain lithium ions, such as V₂O₅ or Cr₃O₈. In the case of using amaterial containing lithium ions as a positive electrode activematerial, the nitride containing lithium and a transition metal can beused for the negative electrode active material by extracting thelithium ions contained in the positive electrode active material inadvance.

Alternatively, a material that causes a conversion reaction can be usedfor the negative electrode active material; for example, a transitionmetal oxide that does not cause an alloy reaction with lithium, such ascobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), may beused. Other examples of the material which causes a conversion reactioninclude oxides such as Fe₂O₃, CuO, Cu₂O, RuO₂, and Cr₂O₃, sulfides suchas CoS_(0.89), NiS, and CuS, nitrides such as Zn₃N₂, Cu₃N, and Ge₃N₄,phosphides such as NiP₂, FeP₂, and CoP₃, and fluorides such as FeF₃ andBiF₃.

The particle diameter of the negative electrode active material ispreferably greater than or equal to 50 nm and less than or equal to 100μm, for example.

Note that a plurality of materials for an active material can becombined at a given proportion both for the positive electrode activematerial layer 101 and the negative electrode active material layer 103.The use of a plurality of materials for the active material layer makesit possible to select fee property of the active material layer in moredetail.

Examples of the conductive additive in the electrode include acetyleneblack (AB), graphite (black lead) particles, carbon nanotubes, graphene,and fullerene.

A network for electric conduction can be formed in the electrode by theconductive additive. The conductive additive also allows maintaining ofa path for electric conduction between the negative electrode activematerial particles. The addition of the conductive additive to thenegative electrode active material layer increases the electricconductivity of the negative electrode active material layer 103.

A typical example of the binder is polyvinylidene fluoride (PVDF), andother examples of the binder include polyimide, polyvinyl chloride,ethylene-propylene-diene polymer, styrene-butadiene rubber,acrylonitrile-butadiene rubber, fluorine rubber, polyvinyl acetate,polymethyl methacrylate, polyethylene, and nitrocellulose.

The content of the binder in the negative electrode active materiallayer 103 is preferably greater than or equal to 1 wt % and less than orequal to 10 wt %, more preferably greater than or equal to 2 wt % andless than or equal to 8 wt %, still more preferably greater than orequal to 3 wt % and less than or equal to 5 wt %. The content of theconductive additive in the negative electrode active material layer 103is preferably greater than or equal to 1 wt % and less than or equal to10 wt %, more preferably greater than or equal to 1 wt % and less thanor equal to 5 wt %.

The negative electrode active material layer 103 is formed over thenegative electrode current collector 102. In the case where the negativeelectrode active material layer 103 is formed by a coating method, thenegative electrode active material, the binder, the conductive additive,and a dispersion medium are mixed to form a slurry, and the slurry isapplied to the negative electrode current collector 102 and dried. Ifnecessary, pressing may be performed after the drying.

The negative electrode current collector 102 can be formed using ahighly conductive material that is not alloyed with a carrier ion of,for example, lithium, such as a metal typified by stainless steel, gold,platinum, iron, copper, titanium, and tantalum or an alloy thereof.Alternatively, a metal element that forms silicide by reacting withsilicon can be used. Examples of the metal element which forms silicideby reacting with silicon include zirconium, titanium, hafnium, vanadium,niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel, andthe like. The current collectors can each have a foil-like shape, aplate-like shape (sheet-like shape), a net-like shape, a cylindricalshape, a coil shape, a punching-metal shape, an expanded-metal shape, orthe like as appropriate. The negative electrode current collector 102preferably has a thickness of 5 μm to 30 μm inclusive. A part of asurface of the electrode current collector may be provided with anundercoat layer using graphite or the like.

Through the above steps, the negative electrode of the lithium-ionstorage battery can be formed.

<<Structure of Separator>>

The separator 104 will be described. The separator 104 may be formedusing a material such as paper, nonwoven fabric, fiberglass, syntheticfiber such as nylon (polyamide), vinylon (polyvinyl alcohol basedfiber), polyester, acrylic, polyolefin, or polyurethane. However, amaterial that does not dissolve in an electrolytic solution describedlater needs to be selected.

More specifically, as a material for the separator 104, any of polymercompounds based on a fluorine-based polymer, polyethers such aspolyethylene oxide and polypropylene oxide, polyolefin such aspolyethylene and polypropylene, polyacrylonitrile, polyvinylidenechloride, polymethyl methacrylate, polymethylacrylate, polyvinylalcohol, polymethacrylonitrile, polyvinyl acetate, polyvinylpyrrolidone,polyethyleneimine, polybutadiene, polystyrene, polyisoprene, andpolyurethane, derivatives thereof, cellulose, paper, nonwoven fabric,and fiberglass can be used either alone or in combination.

The separator 104 needs to have an insulating property of inhibiting thecontact between the electrodes, a property of holding the electrolyticsolution, and ionic conductivity. As a method for forming a film havinga function as a separator, a method for forming a film by stretching isgiven. Examples of the method include a stretching aperture method inwhich a melted polymer material is spread, heat is released from thematerial, and pores are formed by stretching the resulting film in thedirections of two axes parallel to the film.

To set the separator 104 in the storage battery, a method in which theseparator is inserted between the positive electrode and the negativeelectrode can be used. Alternatively, a method in which the separator104 is placed on one of the positive electrode and the negativeelectrode and then the other of the positive electrode and the negativeelectrode is placed thereon can be used. The positive electrode, thenegative electrode, and the separator are provided in the exterior body,and the exterior body is filled with the electrolytic solution, wherebythe storage battery can be fabricated.

The separator 104 with a size large enough to cover each surface ofeither the positive electrode or the negative electrode, in the form ofa sheet or an envelope, may be made to form the electrode wrapped in theseparator 104. In that case, the electrode can be protected frommechanical damages in the fabrication of the storage battery and thehandling of the electrode becomes easier. The electrode wrapped in theseparator and the other electrode are provided in the exterior body, andthe exterior body is filled with the electrolytic solution, whereby thestorage battery can be fabricated. FIG. 1B shows the cross-sectionalstructure of the storage battery including one pair of positive andnegative electrodes.

The separator 104 may include a plurality of layers. Although theseparator 104 can be formed by the above method, the range of thethickness of the film and the size of the pore in the film of theseparator 104 is limited by a material of the separator 104 andmechanical strength of the film. A first separator and a secondseparator each formed by a stretching method may be used together in thestorage battery. The first separator and the second separator can beformed using one or more kinds of material selected from theabove-described materials or materials other than those described above.Characteristics such as the size of the pore in the film, the proportionof the volume of the pores in the film (also referred to as porosity),and the thickness of the film can be determined by film formationconditions, film stretching conditions, and the like. By using the firstseparator and the second separator having different characteristics, theproperties of the separators of the storage battery can be selected morevariously than in the case of using one of the separators.

Furthermore, the storage battery may be flexible. In the case where flowstress is applied to the flexible storage battery, the stress can berelieved by sliding of the first separator and the second separator atthe interface between the first separator and the second separator.Therefore, the structure including a plurality of separators is alsosuitable as a structure of the separator in the flexible storagebattery.

Through the above steps, the separator can be incorporated in thelithium-ion storage battery.

<<Components of Electrolytic Solution>>

The electrolytic solution 105 used in the lithium-ion storage battery ofone embodiment of the present invention is preferably a nonaqueoussolution (solvent) containing an electrolyte (solute).

As a solvent of the electrolytic solution 105, an aprotic organicsolvent is preferably used. For example, one of ethylene carbonate (EC),propylene carbonate (PC), butylene carbonate, chloroethylene carbonate,vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate(DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methylformate, methyl acetate, methyl butyrate, 1,3-dioxane, 1,4-dioxane,dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyldiglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, andsultone can be used, or two or more of these solvents can be used in anappropriate combination in an appropriate ratio.

When a gelled high-molecular material is used as a solvent of theelectrolytic solution 105, safety against liquid leakage and the like isimproved. Furthermore, the lithium-ion storage battery can be thinnerand more lightweight. Typical examples of the gelled high-molecularmaterial include a silicone gel, an acrylic gel, an acrylonitrile gel, apolyethylene oxide-based gel, a polypropylene oxide-based gel, afluorine-based polymer gel, and the like.

Alternatively, the use of one or more kinds of ionic liquids (alsoreferred to as room temperature molten salts) which have features ofnon-flammability and non-evaporability as a solvent of the electrolyticsolution can prevent the lithium-ion storage battery from exploding orcatching fire even when the lithium-ion storage battery internallyshorts out or the internal temperature increases owing to overchargingor the like. Thus, the lithium-ion storage battery has improved safety.

The electrolytic solution used for the storage battery is preferablyhighly purified and contains a small amount of dust particles andelements other than the constituent elements of the electrolyticsolution (hereinafter, also simply referred to as impurities).Specifically, the mass ratio of impurities to the electrolytic solutionis less than or equal to 1%, preferably less than or equal to 0.1%, morepreferably less than or equal to 0.01%.

In the case of using lithium ions as carrier ions, as an electrolytedissolved in the above-described solvent, one of lithium salts such asLiPF₆, LiClO₄, LiAsF₆, LiBF₄, LiAlCl₄, LiSCN, LiBr, LiI, Li₂SO₄,Li₂B₁₀Cl₁₀, Li₂B₁₂Cl₁₂, LiCF₃SO₃, LiC₄F₉SO₃, LiC(CF₃SO₂)₃,LiC(C₂F₅SO₂)₃, LiN(CF₃SO₂)₂, LiN(C₄F₉SO₂)(CF₃SO₂), and LiN(C₂F₅SO₂)₂ canbe used, or two or more of these lithium salts can be used in anappropriate combination at an appropriate ratio.

Although the case where carrier ions are lithium ions in the aboveelectrolyte has been described, carrier ions other than lithium ions canbe used. When the carrier ions other than lithium ions are alkali metalions or alkaline-earth metal ions, instead of lithium in the lithiumsalts, an alkali metal (e.g., sodium or potassium) or an alkaline-earthmetal (e.g., calcium, strontium, barium, beryllium, or magnesium) may beused as the electrolyte.

Note that the electrolytic solution reacts with and corrodes thepositive electrode current collector in some cases. In order to inhibitsuch corrosion, several weight percent of LiPF₆ is preferably added tothe electrolytic solution, in which case a passive film is formed on asurface of the positive electrode current collector and inhibits areaction between the electrolytic solution and the positive electrodecurrent collector. Note that for maintenance of the cycle life at hightemperatures the concentration of LiPF₆ is less than or equal to 10 wt%, preferably less than or equal to 5 wt %, and more preferably lessthan or equal to 3 wt % in order that the positive electrode materiallayer is not dissolved.

<<Structure of Exterior Body>>

Next, the exterior body 207 will be described. As the exterior body 207,a film having a three-layer structure can be used, for example. In thethree-layer structure, a highly flexible metal thin film of aluminum,stainless steel, copper, nickel, or the like is provided over a filmformed of a material such as polyethylene, polypropylene, polycarbonate,ionomer, or polyamide, and an insulating synthetic resin film of apolyamide-based resin, a polyester based resin, or the like is providedas the outer surface of the exterior body over the metal thin film canbe used. With such a three-layer structure, the passage of anelectrolytic solution and a gas can be blocked and an insulatingproperty and resistance to the electrolytic solution can be provided.The exterior body is folded inside in two, or two exterior bodies arestacked with the inner surfaces facing each other, in which caseapplication of heat melts the materials on the overlapping innersurfaces to cause fusion bonding between the two exterior bodies. Inthis manner, a sealing structure can be formed.

A portion where the sealing structure is formed by fusion bonding or thelike of the exterior body is referred to as a sealing portion. In thecase where the exterior body is folded inside in two, the sealingportion is formed in the place other than the fold, and a first regionof the exterior body and a second region of the exterior body thatoverlaps with the first region are fusion-bonded, for example. In thecase where two exterior bodies are stacked, the sealing portion isformed along the entire outer region by heat fusion bonding or the like.

<<Flexible Storage Battery>>

When a flexible material is selected from materials of the membersdescribed in this embodiment and used, a flexible lithium-ion storagebattery can be fabricated. Deformable devices are currently under activeresearch and development. For such devices, flexible storage batteriesare demanded.

In the case of bending a storage battery in which components 1805including electrodes and an electrolytic solution is sandwiched betweentwo films as exterior bodies, a radius 1802 of curvature of a film 1801close to a center 1800 of curvature of the storage battery is smallerthan a radius 1804 of curvature of a film 1803 far from the center 1800of curvature (FIG. 2A). When the storage battery is curved and has anare-shaped cross section, compressive stress is applied to a surface ofthe film on the side closer to the center 1800 of curvature and tensilestress is applied to a surface of the film on the side farther from thecenter 1800 of curvature (FIG. 2B).

When the flexible lithium-ion storage battery is changed in form, greatstress is imposed on the exterior bodies. However, by forming a patternincluding projections or depressions on surfaces of the exterior bodies,the influence of a strain can be reduced to be acceptable even whencompressive stress and tensile stress are applied because of deformationof the storage battery. For this reason, the storage battery can changeits form such that the exterior body on the side closer to the center ofcurvature has a curvature radius greater than or equal to 50 mm,preferably greater than or equal to 30 mm.

Description is given of the radius of curvature of a surface withreference to FIGS. 3A to 3C. In FIG. 3A, on a plane 1701 along which acurved surface 1700 is cut, part of a curve 1702 forming the curvedsurface 1700 is approximate to an arc of a circle, and the radius of thecircle is referred to as a radius 1703 of curvature and the center ofthe circle is referred to as a center 1704 of curvature. FIG. 3B is atop view of the curved surface 1700. FIG. 3C is a cross-sectional viewof the curved surface 1700 taken along the plane 1701. When a curvedsurface is cut along a plane, the radius of curvature of a curve in across section differs depending on the angle between the curved surfaceand the plane or on the cut position, and the smallest radius ofcurvature is defined as the radius of curvature of a surface in thisspecification and the like.

Note that the cross-sectional shape of the storage battery is notlimited to a simple arc shape, and the cross section can be partlyarc-shaped; for example, a shape illustrated in FIG. 2C, a wavy shapeillustrated in FIG. 2D, or an S shape can be used. When the curvedsurface of the storage battery has a shape with a plurality of centersof curvature, the storage battery can change its form such that a curvedsurface with the smallest radius of curvature among radii of curvaturewith respect to the plurality of centers of curvature, which is asurface of the exterior body on the side closer to the center ofcurvature, has a curvature radius greater than or equal to 50 mm,preferably greater than or equal to 30 mm.

<<Assembly of Storage Battery and Aging>>

Next, the above components are combined and enclosed in the exteriorbody 207, so that the positive electrode current collector 100, thepositive electrode active material layer 101, the separator 104, thenegative electrode active material layer 103, and the negative electrodecurrent collector 102 are stacked and enclosed in the exterior body 207together with the electrolytic solution 105 as illustrated in FIGS. 1Aand 1B.

Then, an aging process is performed. First, environmental temperature iskept at about room temperature for example, and constant current chargeis performed to a predetermined voltage at a low rate. Next, a gasgenerated in a region inside the exterior body by charging is releasedoutside the exterior body, and then charge is performed at a rate higherthan that of the initial charge.

After that, the storage battery is kept at high temperatures for a longtime. For example, the storage battery is kept at higher than or equalto 40° C. for longer than or equal to 24 hours.

After the storage battery is kept at high temperatures for a long time,gases generated in a region inside the exterior body is released again.Furthermore, the storage battery is discharged at a rate of 0.2 C atroom temperature, charged at the same rate, discharged at the same rateagain, and further charged at the same rate. Then, discharge isperformed at the same rate. Through these steps, the aging process isterminated.

In the aforementioned manner, the storage battery of one embodiment ofthe present invention can be fabricated.

This embodiment can be implemented in combination with any of the otherembodiments as appropriate.

Note that in the case where at least one specific example is describedin a diagram or text described in one embodiment in this specificationand the like, it will be readily appreciated by those skilled in the artthat a broader concept of the specific example can be derived.Therefore, in the diagram or the text described in one embodiment, inthe case where at least one specific example is described, a broaderconcept of the specific example is disclosed as one embodiment of theinvention, and one embodiment of the invention can be constituted. Theembodiment of the present invention is clear.

Note that in this specification and the like, what is illustrated in atleast a diagram (which may be part of the diagram) is disclosed as oneembodiment of the invention, and one embodiment of the invention can beconstituted. Therefore, when certain contents are described in adiagram, the contents are disclosed as one embodiment of the inventioneven when the contents are not described with text, and one embodimentof the invention can be constituted. In a similar manner, part of adiagram, which is taken out from the diagram, is disclosed as oneembodiment of the invention, and one embodiment of the invention can beconstituted. The embodiment of the present invention is clear.

In this embodiment, one embodiment of the present invention has beendescribed. Other embodiments of the present invention will be describedin other embodiments. Note that one embodiment of the present inventionis not limited thereto. In other words, various embodiments of theinvention are described in this embodiment and the other embodiments,and one embodiment of the present invention is not limited to aparticular embodiment. For example, although an example of use in alithium-ion secondary battery is described in this embodiment, oneembodiment of the present invention is not limited thereto. Depending oncircumstances or conditions, application of one embodiment of thepresent invention to a variety of secondary batteries such as a leadstorage battery, a lithium-ion polymer secondary battery, anickel-hydrogen storage battery, a nickel-cadmium storage battery, anickel-iron storage battery, a nickel-zinc storage battery, a silveroxide-zinc storage battery, a solid-state battery, and an air battery isalso possible. Depending on circumstances or conditions, one embodimentof the present invention is not necessarily applied to a lithium-ionsecondary battery, for example.

Embodiment 2

In this embodiment, an example of the configuration described in theabove embodiment in which an exterior body of a lithium-ion storagebattery is provided with wirings and examples of the wirings and acircuit for detecting a fracture of the lithium-ion storage battery willbe described.

FIG. 24A is a schematic diagram of a laminated storage battery includingan exterior body 5007 that is provided with wirings 5006. FIG. 24B is across-sectional view along the dashed-dotted line X1-X2 in FIG. 24A. Theexterior body 5007 of the lithium-ion storage battery 110 illustrated inFIGS. 24A and 24B is provided with the wirings 5006 along the shape ofthe exterior body 5007 in order to prevent damage by fatigue due todeformation. The exterior body 5007 is also provided with a circuit 5008for detecting damage to the wirings 5006, such as a fracture.

The wirings 5006 can be formed using a material that is less resistantto deformation than a material of a component to be protected from beingdamaged, that is, a material of the exterior body 5007. The wirings 5006can be provided in the following manner: wirings prepared in advance areattached to the exterior body 5007; or a conductive paste or slurry isapplied or printed to have a predetermined shape on the exterior body5007 and dried. Furthermore, protective films for preventing damage by acause other than fatigue due to deformation may be provided over thewirings 5006.

As a material of the exterior body 5007, for example, a film having athree-layer structure in which a highly flexible metal thin film ofaluminum, stainless steel, copper, nickel, or the like is provided overa film formed of a material such as polyethylene, polypropylene,polycarbonate, ionomor, or polyamide, and an insulating synthetic resinfilm of a polyamide-based resin, a polyester-based resin, or the like isprovided as the outer surface of the exterior body over the metal thinfilm can be used as described in Embodiment 1. In the case where such afilm with a three-layer structure is used as the exterior body, whenrepeated changes in the form of the exterior body increase fatigue(damage), the metal thin layer might be damaged. Thus, the wirings 5006should be less resistant to deformation than the metal thin layer.

When the exterior body in the form of a film with a three-layerstructure is used, a material that has lower mechanical strength thanthe metal thin layer can be used to form the wiring 5006 that is moreeasily breakable than the metal thin layer. A variety of methods tomeasure mechanical strength are known, and a material whose strength isfound to be low by any of the measurement methods is used.

Although the wirings 5006 are provided at two positions in FIG. 24A, forexample, the number of the wirings is not limited to two. Terminals of aseries of wirings 5006 are electrically connected to the circuit 5008.

Although the circuit 5008 is provided over the exterior body 5007 inFIG. 24A, for example, there is no limitation on the place where thecircuit 5008 is provided. The circuit 5008 may be provided inside thelithium-ion storage battery 110, for example. Alternatively, the circuit5008 may be provided outside the lithium-ion storage battery 110.Alternatively, the circuit 5008 may be provided over the same substrateas a battery management unit BMU of the lithium-ion storage battery 110.Alternatively, the circuit 5008 may be provided in an electronic devicethat is supplied with power from the lithium-ion storage battery 110.Note that power for driving the circuit 5008 can be directly suppliedfrom the lithium-ion storage battery 110. In that case, the voltage ofthe lithium-ion storage battery 110 is raised or lowered as needed andsupplied.

A circuit diagram in FIG. 25A illustrates the connection between thecircuit 5008 and the wiring 5006 in FIGS. 24A and 24B. Note that in FIG.25A, a battery cell 5011 inside the exterior body 5007, a positiveterminal, a negative terminal, and a terminal for outputting a signalfor indicating presence or absence of damage such as a fracture areillustrated for explanation. The positive terminal, the negativeterminal, and the terminal are provided on the side where an FPC fortaking out the signal to the outside is provided, and the circuit 5008and the wiring 5006 are provided on the exterior body 5007 side.

In FIG. 25A, one terminal of the wiring 5006 is electrically connectedto a positive electrode of the battery cell 5011. The other terminal ofthe wiring 5006 is electrically connected to the positive electrode ofthe battery cell 5011 through the wiring 5006.

The circuit 5008 is connected to each of the one terminal and the otherterminal of the wiring 5006. The circuit 5008 has a function ofoutputting a signal in accordance with presence or absence of damage tothe wiring 5006, such as a fraction. The circuit 5008 can detect adifference in potential between the one terminal and the other terminalof the wiring 5006 and output a signal to the terminal S_(alert), forexample.

FIG. 25B illustrates the configuration of the circuit 5008. The circuit5008 includes an exclusive OR circuit 5009 and a D latch 5010. Note thata transistor included in the circuit 5008 can be formed using an oxidesemiconductor in a channel formation region, and the CAAC-OS filmdescribed above can be used as the oxide semiconductor.

The exclusive OR circuit 5009 is supplied with a potential 5006_1 of theone terminal of the wiring 5006 and a potential 5006_2 of the otherterminal of the wiring 5006. An output of the exclusive OR circuit 5009is supplied to a D terminal and a CK terminal of the D latch 5010. Anoutput of the D latch 5010 is supplied to the terminal S_(alert) from aQ terminal. A signal for indicating presence or absence of damage suchas a fracture that is output from the terminal S_(alert) is output to anexternal circuit.

The circuit 5008 outputs a low-level (low-potential) signal when thewiring 5006 has no damage such as a fracture. The wiring 5006 having nodamage such as a fracture has low resistance; thus, the potential 5006_1and the potential 5006_2 are equal to each other. In this case, theexclusive OR circuit 5009 outputs a low potential, and the low potentialis input to the D terminal and the CK terminal of the D latch 5010, andthe low potential is output from the Q terminal of the D latch 5010.These are operations in a normal state where the wiring 5006 has nodamage such as a fracture.

On the other hand, the circuit 5008 outputs a high-level(high-potential) signal when the wiring 5006 has damage such as afracture. When the wirings 5006 and the exterior body 5007 are deformedand fatigue (damage) accumulates because of repeated deformation of thelithium-ion storage battery 110, the wiring 5006 is damaged (e.g.,fractured) first, increasing electric resistance. Thus, supply of chargefrom the battery cell 5011 to the other terminal of the wiring 5006 isstopped, so that the potential 5006_2 is decreased by release of chargeto the outside. In contrast, there is supply of charge from the batterycell 5011 to the one terminal of the wiring 5006; therefore, thepotential 5006_1 can be different from the potential 5006_2. When thepotential 5006_1 and the potential 5006_2 are different from each other,the exclusive OR circuit 5009 outputs a high potential, the highpotential is input to the D terminal and the CK terminal of the D latch5010, and the high potential is output from the Q terminal of the Dlatch 5010. These are operations in a state where the wiring 5006 hasdamage such as a fracture.

When the wiring 5006 is damaged (e.g., fractured), the circuit 5008outputs the high potential as a signal to an external circuit, therebynotifying a user of an abnormal state of the wiring 5006 to alerthim/her to stop the use of the lithium-ion storage battery 110 andreplace it with a new one. Since the use of the lithium-ion storagebattery 110 can be stopped before the exterior body 5007 is damaged, anaccident due to damage to the exterior body 5007 can be prevented. Notethat the signal is generated by the D latch 5010 and thus keeps beingoutput once it is output.

Although the method to detect damage to the wiring with the use of thecircuit has been described in this embodiment, a method to detect damageto the wiring is not limited thereto. It is possible to utilize a changein any of a variety of physical properties such as thermal conductivityand volume due to accumulated fatigue of (damage to) the wiring.

In the aforementioned manner, the lithium-ion storage battery of oneembodiment of the present invention can prevent an accident of afracture of a component due to accumulated fatigue (damage) caused byrepeated deformation.

This embodiment can be implemented in combination with any of the otherembodiments as appropriate.

Embodiment 3

In this embodiment, structures of a storage batteries of embodiments ofthe present invention will be described with reference to FIGS. 4A to4C, FIGS. 5A and 5B, and FIGS. 6A and 6B.

<<Coin-Type Storage Battery>>

FIG. 4A is an external view of a coin-type (single-layer flat type)storage battery, and FIG. 4B is a cross-sectional view thereof.

In a coin-type storage battery 300, a positive electrode can 301doubling as a positive electrode terminal and a negative electrode can302 doubling as a negative electrode terminal are insulated from eachother and sealed by a gasket 303 made of polypropylene or the like. Apositive electrode 304 includes a positive electrode current collector305 and a positive electrode active material layer 306 provided incontact with the positive electrode current collector 305. The positiveelectrode active material layer 306 may further include a binder forincreasing adhesion of positive electrode active materials, a conductiveadditive for increasing the conductivity of the positive electrodeactive material layer, and the like in addition to the active materials.

A negative electrode 307 includes a negative electrode current collector308 and a negative electrode active material layer 309 provided incontact with the negative electrode current collector 308. The negativeelectrode active material layer 309 may further include a binder forincreasing adhesion of negative electrode active materials, a conductiveadditive for increasing the conductivity of the negative electrodeactive material layer, and the like in addition to the negativeelectrode active materials. A separator 310 and an electrolyte (notillustrated) are provided between the positive electrode active materiallayer 306 and the negative electrode active material layer 309.

The materials described in Embodiment 1 can be used for the components.

For the positive electrode can 301 and the negative electrode can 302, ametal having a corrosion-resistant property to an electrolytic solution,such as nickel or titanium, an alloy of such a metal, or an alloy ofsuch a metal and another metal (e.g., stainless steel or the like) canbe used. Alternatively, the positive electrode can 301 and the negativeelectrode can 302 are preferably covered with nickel or the like inorder to prevent corrosion due to the electrolytic solution. Thepositive electrode can 301 and the negative electrode can 302 areelectrically connected to the positive electrode 304 and the negativeelectrode 307, respectively.

The negative electrode 307, the positive electrode 304, and theseparator 310 are immersed in the electrolytic solution. Then, asillustrated in FIG. 4B, the positive electrode 304, the separator 310,the negative electrode 307, and the negative electrode can 302 arestacked in this order with the positive electrode can 301 positioned atthe bottom, and the positive electrode can 301 and the negativeelectrode can 302 are subjected to pressure bonding with the gasket 303interposed therebetween. In such a manner, the coin-type storage battery300 can be manufactured.

Here, a current flow in charging a storage battery will be describedwith reference to FIG. 4C. When a storage battery using lithium isregarded as a closed circuit, lithium ions transfer and a current flowsin the same direction. Note that in the storage battery using lithium,an anode and a cathode change places in charge and discharge, and anoxidation reaction and a reduction reaction occur on the correspondingsides; hence, an electrode with a high redox potential is called apositive electrode and an electrode with a low redox potential is calleda negative electrode. For this reason, in this specification, thepositive electrode is referred to as a “positive electrode” and thenegative electrode is referred to as a “negative electrode” in all thecases where charge is performed, discharge is performed, a reverse pulsecurrent is supplied, and a charging current is supplied. The use of theterms “anode” and “cathode” related to an oxidation reaction and areduction reaction might cause confusion because the anode and thecathode change places at the time of charging and discharging. Thus, theterms “anode” and “cathode” are not used in this specification. If theterm “anode” or “cathode” is used, it should be mentioned that the anodeor the cathode is which of the one at the time of charging or the one atthe time of discharging and corresponds to which of a positive electrodeor a negative electrode.

Two terminals in FIG. 4C are connected to a charger, and a storagebattery 400 is charged. As the charge of the storage battery 400proceeds, a potential difference between electrodes increases. In FIG.4C, the direction in which the current flows from one terminal outsidethe storage battery 400 to a positive electrode 402, flows from thepositive electrode 402 to a negative electrode 404 in the storagebattery 400, and flows from the negative electrode 404 to the otherterminal outside the storage battery 400 is the positive direction.

<<Cylindrical Storage Battery>>

Next, an example of a cylindrical storage battery will be described withreference to FIGS. 5A and 5B. The cylindrical storage battery 600includes a positive electrode cap (battery cap) 601 on the upper surfaceand a battery can (outer can) 602 on the side surface and the lowersurface. The positive electrode cap 601 and the battery can 602 areinsulated from each other by a gasket (insulating gasket) 610.

FIG. 5B is a diagram schematically illustrating a cross section of thecylindrical storage battery. Inside the battery can 602 having a hollowcylindrical shape, a battery element in which a strip-like positiveelectrode 604 and a strip-like negative electrode 606 are wound with astripe-like separator 605 interposed therebetween is provided. Althoughnot illustrated, the battery element is wound around a center pin. Oneend of the battery can 602 is close and the other end thereof is open.For the battery can 602, a metal having a corrosion-resistant propertyto an electrolytic solution, such as nickel or titanium, an alloy ofsuch a metal, or an alloy of such a metal and another metal (e.g.,stainless steel or the like) can be used. Alternatively, the battery can602 is preferably covered with nickel or the like in order to preventcorrosion due to the electrolytic solution. Inside the battery can 602,the battery element in which the positive electrode, the negativeelectrode, and the separator are wound is provided between a pair ofinsulating plates 608 and 609 that face each other. Furthermore, anonaqueous electrolytic solution (not illustrated) is injected insidethe battery can 602 provided with the battery element. As the nonaqueouselectrolytic solution, a nonaqueous electrolytic solution that issimilar to that of the coin-type storage battery can be used.

Although the positive electrode 604 and the negative electrode 606 canbe formed in a manner similar to that of the positive electrode and thenegative electrode of the coin-type storage battery described above, thedifference lies in that, since the positive electrode and the negativeelectrode of the cylindrical storage battery are wound, active materialsare formed on both sides of the current collectors. A positive electrodeterminal (positive electrode current collecting tab) 603 is connected tothe positive electrode 604, and a negative electrode terminal (negativeelectrode current collecting tab) 607 is connected to the negativeelectrode 606. Both the positive electrode terminal 603 and the negativeelectrode terminal 607 can be formed using a metal material such asaluminum. The positive electrode terminal 603 and the negative electrodeterminal 607 are resistance-welded to a safety valve mechanism 612 andthe bottom of the battery can 602, respectively. The safety valvemechanism 612 is electrically connected to the positive electrode cap601 through a positive temperature coefficient (PTC) element 611. Thesafety valve mechanism 612 cuts off electrical connection between thepositive electrode cap 601 and the positive electrode 604 when theinternal pressure of the battery exceeds a predetermined thresholdvalue. The PTC element 611, which serves as a thermally sensitiveresistor whose resistance increases as temperature rises, limits theamount of current by increasing the resistance, in order to preventabnormal heat generation. Note that barium titanate (BaTiO₃)-basedsemiconductor ceramic can be used for the PTC element.

<<Laminated Storage Battery>>

Next, an example of a laminated storage battery will be described withreference to FIG. 6A. When a flexible laminated storage battery is usedin an electronic device at least part of which is flexible, the storagebattery can be bent as the electronic device is bent.

A laminated storage battery 500 illustrated in FIG. 6A includes apositive electrode 503 including a positive electrode current collector501 and a positive electrode active material layer 502, a negativeelectrode 506 including a negative electrode current collector 504 and anegative electrode active material layer 505, a separator 507, anelectrolytic solution 508, and an exterior body 509. The separator 507is provided between the positive electrode 503 and the negativeelectrode 506 in the exterior body 509. The electrolytic solution 508 isincluded in the exterior body 509. The electrolytic solution describedin Embodiment 1 can be used as the electrolytic solution 508.

In the laminated storage battery 500 illustrated in FIG. 6A, thepositive electrode current collector 501 and the negative electrodecurrent collector 504 also serve as terminals for an electrical contactwith an external portion. For this reason, each of the positiveelectrode current collector 501 and the negative electrode currentcollector 504 may be arranged so that part of the positive electrodecurrent collector 501 and part of the negative electrode currentcollector 504 are exposed to the outside of the exterior body 509.Alternatively, a tab electrode and the positive electrode currentcollector 501 or the negative electrode current collector 504 may bebonded to each other by ultrasonic welding, and instead of the positiveelectrode current collector 501 and the negative electrode currentcollector 504, the tab electrode may be exposed to the outside of theexterior body 509.

As the exterior body 509 in the laminated storage battery 500, forexample, a laminate film having a three-layer structure in which ahighly flexible metal thin film of aluminum, stainless steel, copper,nickel, or the like is provided over a film formed of a material such aspolyethylene, polypropylene, polycarbonate, ionomer, or polyamide, andan insulating synthetic resin film of a polyamide-based resin, apolyester-based resin, or the like is provided as the outer surface ofthe exterior body over the metal thin film can be used.

FIG. 6B illustrates an example of a cross-sectional structure of thelaminated storage battery 500. Although FIG. 6A illustrates an exampleof including only two current collectors for simplicity, the actualbattery includes a plurality of electrode layers.

The example in FIG. 6B includes 16 electrode layers. The laminatedstorage battery 500 has flexibility even though including 16 electrodelayers. In FIG. 6B, 8 negative electrode current collectors 504 and 8positive electrode current collectors 501 are included. Note that FIG.6B illustrates a crass section of a lead portion of the negativeelectrode, and 8 negative electrode current collectors 504 are bonded toeach other by ultrasonic welding. It is needless to say that the numberof electrode layers is not limited to 16, and may be more than 16 orless than 16. In the case of using a large number of electrode layers,the storage battery can have high capacity. In contrast, in the case ofusing a small number of electrode layers, the storage battery can have asmall thickness and high flexibility.

FIGS. 7 and 8 each illustrate an example of the external view of thelaminated storage battery 500. In FIGS. 7 and 8, the positive electrode503, the negative electrode 506, the separator 507, the exterior body509. a positive electrode tab electrode 510, and a negative electrodetab electrode 511 are included.

FIG. 9A illustrates the external views of the positive electrode 503 andthe negative electrode 506. The positive electrode 503 includes thepositive electrode current collector 501, and the positive electrodeactive material layer 502 is formed over a surface of the positiveelectrode current collector 501. The positive electrode 503 alsoincludes a region where the positive electrode current collector 501 ispartly exposed (referred to as a tab region). The negative electrode 506includes the negative electrode current collector 504, and the negativeelectrode active material layer 505 is formed over a surface of thenegative electrode current collector 504. The negative electrode 506also includes a region where the negative electrode current collector504 is partly exposed, that is, a tab region. The areas and shapes ofthe tab regions included in the positive electrode and negativeelectrode are not limited to those illustrated in FIG. 9A.

<<Method for Fabricating Laminated Storage Battery>>

Here, an example of a method for fabricating the laminated storagebattery whose external view is illustrated in FIG. 7 will be describedwith reference to FIGS. 9B and 9C.

First, the negative electrode 506, the separator 507, and the positiveelectrode 503 are stacked. FIG. 9B illustrates a stack including thenegative electrode 506, the separator 507, and the positive electrode503. The battery described here as an example includes 5 negativeelectrodes and 4 positive electrodes. Next, the tab regions of thepositive electrodes 503 are bonded to each other, and the tab region ofthe positive electrode of the outermost surface and the positiveelectrode tab electrode 510 are bonded to each other. The bonding can beperformed by ultrasonic welding, for example. In a similar manner, thetab regions of the negative electrodes 506 are bonded to each other, andthe tab region of the negative electrode of the outermost surface andthe negative electrode tab electrode 511 are bonded to each other.

After that, the negative electrode 506, the separator 507, and thepositive electrode 503 are placed over the exterior body 509.

Subsequently, the exterior body 509 is folded along a dashed line asillustrated in FIG. 9C. Then, the outer edge of the exterior body 509 isbonded. The bonding can be performed by thermocompression, for example.At this time, a part (or one side) of the exterior body 509 is leftunbonded (to provide an inlet) so that the electrolytic solution 508 canbe introduced later.

Next, the electrolytic solution 508 is introduced into the exterior body509 from the inlet of the exterior body 509. The electrolytic solution508 is preferably introduced in a reduced pressure atmosphere or in aninert gas atmosphere. Lastly, the inlet is bonded. In the above manner,the laminated storage battery 500 can be fabricated.

Note that in this embodiment, the coin-type storage battery, thelaminated storage battery, and the cylindrical storage battery are givenas examples of the storage battery; however, any of storage batterieswith a variety of shapes, such as a sealed storage battery and asquare-type storage battery, can be used. Furthermore, a structure inwhich a plurality of positive electrodes, a plurality of negativeelectrodes, and a plurality of separators are stacked or wound may beemployed.

FIGS. 10A to 10E illustrate examples of electronic devices includingflexible laminated storage batteries. Examples of electronic deviceseach including a flexible storage battery include television devices(also referred to as televisions or television receivers), monitors ofcomputers or the like, cameras such as digital cameras and digital videocameras, digital photo frames, mobile phones (also referred to as mobilephones or mobile phone devices), portable game machines, portableinformation terminals, audio reproducing devices, and large gamemachines such as pachinko machines.

In addition, a flexible storage battery can be incorporated along acurved inside/outside wall surface of a house or a building or a curvedinterior/exterior surface of a car.

FIG. 10A illustrates an example of a mobile phone. A mobile phone 7400is provided with a display portion 7402 incorporated in a housing 7401,an operation button 7403, an external connection port 7404, a speaker7405, a microphone 7406, and the like. Note that the mobile phone 7400includes a storage battery 7407.

FIG. 10B illustrates the mobile phone 7400 that is bent. When the wholemobile phone 7400 is bent by the external force, the storage battery7407 included in the mobile phone 7400 is also bent. FIG. 10Cillustrates the bent storage battery 7407. The storage battery 7407 is alaminated storage battery.

FIG. 10D illustrates an example of a bangle display device. A portabledisplay device 7100 includes a housing 7101, a display portion 7102, anoperation button 7103, and a storage battery 7104. FIG. 10E illustratesthe bent storage battery 7104.

<<Structural Examples of Storage Batteries>>

Structural examples of storage batteries will be described withreference to FIGS. 11A and 11B, FIGS. 12A1 to 12B2, FIGS. 13A and 13B,FIGS. 14A and 14B, and FIG. 15.

FIGS. 11A and 11B are external views of a storage battery. The storagebattery includes a circuit board 900 and a storage battery 913. A label910 is attached to the storage battery 913. As shown in FIG. 11B, thestorage battery further includes a terminal 951, a terminal 952, anantenna 914, and an antenna 915.

The circuit board 900 includes terminals 911 and a circuit 912. Theterminals 911 are connected to the terminals 951 and 952, the antennas914 and 915, and the circuit 912. Note that a plurality of terminals 911serving as a control signal input terminal, a power supply terminal, andthe like may be provided.

The circuit 912 may be provided on the rear surface of the circuit board900. The shape of each of the antennas 914 and 915 is not limited to acoil shape and may be a linear shape or a plate shape. Further, a planarantenna, an aperture antenna, a traveling-wave antenna, an EH antenna, amagnetic-field antenna, or a dielectric antenna may be used.Alternatively, the antenna 914 or the antenna 915 may be a flat-plateconductor. The flat-plate conductor can serve as one of conductors forelectric field coupling. That is, the antenna 914 or the antenna 915 canserve as one of two conductors of a capacitor. Thus, electric power canbe transmitted and received not only by an electromagnetic field or amagnetic field but also by an electric field.

The line width of the antenna 914 is preferably larger than that of theantenna 915. This makes it possible to increase the amount of electricpower received by the antenna 914.

The storage battery includes a layer 916 between the storage battery 913and the antennas 914 and 915. The layer 916 may have a function ofpreventing an adverse effect on an electromagnetic field by the storagebattery 913. As the layer 916. for example, a magnetic body can be used.

Note that the structure of the storage battery is not limited to thatshown in FIGS. 11A and 11B.

For example, as shown in FIGS. 12A1 and 12A2, two opposite surfaces ofthe storage battery 913 in FIGS. 11A and 11B may be provided withrespective antennas. FIG. 12A1 is an external view showing one side ofthe opposite surfaces, and FIG. 12A2 is an external view showing theother side of the opposite surfaces. For portions similar to those inFIGS. 11A and 11B, a description of the storage battery illustrated inFIGS. 11A and 11B can be referred to as appropriate.

As illustrated in FIG. 12A1, the antenna 914 is provided on one of theopposite surfaces of the storage battery 913 with the layer 916interposed therebetween, and as illustrated in FIG. 12A2, the antenna915 is provided on the other of the opposite surfaces of the storagebattery 913 with a layer 917 interposed therebetween. The layer 917 mayhave a function of preventing an adverse effect on an electromagneticfield by the storage battery 913. As the layer 917, for example, amagnetic body can be used.

With the above structure, both of the antennas 914 and 915 can beincreased in size.

Alternatively, as illustrated in FIGS. 12B1 and 12B2, two oppositesurfaces of the storage battery 913 in FIGS. 11A and 11B may be providedwith different types of antennas. FIG. 12B1 is an external view showingone side of the opposite surfaces, and FIG. 12B2 is an external viewshowing the other side of the opposite surfaces. For portions similar tothose in FIGS. 11A and 11B, a description of the storage batteryillustrated in FIGS. 11A and 11B can be referred to as appropriate.

As illustrated in FIG. 12B1, the antenna 914 is provided on one of theopposite surfaces of the storage battery 913 with the layer 916interposed therebetween, and as illustrated in FIG. 12B2, an antenna 918is provided on the other of the opposite surfaces of the storage battery913 with the layer 917 interposed therebetween. The antenna 918 has afunction of communicating data with an external device, for example. Anantenna with a shape that can be applied to the antennas 914 and 915,for example, can be used as the antenna 918. As a system forcommunication using the antenna 918 between the storage battery andanother device, a response method that can be used between the storagebattery and another device, such as NFC, can be employed.

Alternatively, as illustrated in FIG. 13A, the storage battery 913 inFIGS. 11A and 11B may be provided with a display device 920. The displaydevice 920 is electrically connected to the terminal 911 via a terminal919. It is possible that the label 910 is not provided in a portionwhere the display device 920 is provided. For portions similar to thosein FIGS. 11A and 11B, a description of the storage battery illustratedin FIGS. 11A and 11B can be referred to as appropriate.

The display device 920 can display, for example, an image showingwhether charge is being carried out, an image showing the amount ofstored power, or the like. As the display device 920, electronic paper,a liquid crystal display device, an electroluminescent (EL) displaydevice, or the like can be used. For example, the use of electronicpaper can reduce power consumption of the display device 920.

Alternatively, as illustrated in FIG. 13B, the storage battery 913illustrated in FIGS. 11A and 11B may be provided with a sensor 921. Thesensor 921 is electrically connected to the terminal 911 via a terminal922. For portions similar to those in FIGS. 11A and 11B, a descriptionof the storage battery illustrated in FIGS. 11A and 11B can be referredto as appropriate.

The sensor 921 has a function of measuring, for example, displacement,position, speed, acceleration, angular velocity, rotational frequency,distance, light, liquid, magnetism, temperature, chemical substance,sound, time, hardness, electric field, electric current, voltage,electric power, radiation, flow rate, humidity, gradient, oscillation,odor, or infrared rays. With the sensor 921, for example, data on anenvironment (e.g., temperature) where the storage battery is placed canbe determined and stored in a memory inside the circuit 912.

Furthermore, structural examples of the storage battery 913 will bedescribed with reference to FIGS. 14A and 14B and FIG. 15.

The storage battery 913 illustrated in FIG. 14A includes a wound body950 provided with the terminals 951 and 952 inside a housing 930. Thewound body 950 is soaked in an electrolytic solution inside the housing930. The terminal 952 is in contact with the housing 930. An insulatoror the like prevents contact between the terminal 951 and the housing930. Note that in FIG. 14A, the housing 930 divided into two pieces isillustrated for convenience; however, in the actual structure, the woundbody 950 is covered with the housing 930 and the terminals 951 and 952extend to the outside of the housing 930. For the housing 930, a metalmaterial or a resin material can be used.

Note that as illustrated in FIG. 14B, the housing 930 in FIG. 14A may beformed using a plurality of materials. For example, in the storagebattery 913 in FIG. 14B, a housing 930 a and a housing 930 b are bondedto each other and the wound body 950 is provided in a region surroundedby the housing 930 a and the housing 930 b.

For the housing 930 a, an insulating material such as an organic resincan be used. In particular, when a material such as an organic resin isused for the side on which an antenna is formed, blocking of an electricfield by the storage battery 913 can be prevented. When an electricfield is not significantly blocked by the housing 930 a, an antenna suchas the antennas 914 and 915 may be provided inside the housing 930 a.For the housing 930 b, a metal material can be used, for example.

FIG. 15 illustrates the structure of the wound body 950. The wound body950 includes a negative electrode 931, a positive electrode 932, and aseparator 933. The wound body 950 is obtained by winding a sheet of astack in which the negative electrode 931 overlaps with the positiveelectrode 932 with the separator 933 provided therebetween. Note that aplurality of stacks of the negative electrode 931, the positiveelectrode 932, and the separator 933 may be stacked.

The negative electrode 931 is connected to the terminal 911 in FIGS. 11Aand 11B via one of the terminals 951 and 952. The positive electrode 932is connected to the terminal 911 in FIGS. 11A and 11B via the other ofthe terminals 951 and 952.

<<Examples of Electronic Devices: Vehicles>>

Next, examples where a storage battery is used in a vehicle will bedescribed. The use of storage batteries in vehicles enables productionof next-generation clean energy vehicles such as hybrid electricvehicles (HEVs), electric vehicles (EVs), and plug-in hybrid electricvehicles (PHEVs).

FIGS. 16A and 16B each illustrate an example of a vehicle using oneembodiment of the present invention. An automobile 8100 illustrated inFIG. 16A is an electric vehicle that runs on the power of an electricmotor. Alternatively, the automobile 8100 is a hybrid electric vehiclecapable of driving appropriately using either the electric motor or theengine. One embodiment of the present invention can provide ahigh-mileage vehicle. The automobile 8100 includes the storage battery.The storage battery is used not only for driving the electric motor, butalso for supplying electric power to a light-emitting device such as aheadlight 8101 or a room light (not illustrated).

The storage battery can also supply electric power to a display deviceof a speedometer, a tachometer, or the like included in the automobile8100. Furthermore, the storage battery can supply electric power to asemiconductor device included in the automobile 8100, such as anavigation system.

FIG. 16B illustrates an automobile 8200 including the storage battery.The automobile 8200 can be charged when the storage battery is suppliedwith electric power through external charging equipment by a plug-insystem, a contactless power feeding system, or the like. In FIG. 16B, astorage battery included in the automobile 8200 is charged with the useof a ground-based charging apparatus 8021 through a cable 8022. Incharging, a given method may be employed as a charging method, thestandard of a connector, or the like as appropriate. The ground-basedcharging apparatus 8021 may be a charging station provided in a commercefacility or a power source in a house. For example, with the use of aplug-in technique, the storage battery included in the automobile 8200can be charged by being supplied with electric power from outside. Thecharging can be performed by converting AC electric power into DCelectric power through a converter such as an AC-DC converter.

Furthermore, although not illustrated, the vehicle may include a powerreceiving device so that it can be charged by being supplied withelectric power from an above-ground power transmitting device in acontactless manner. In the case of the contactless power feeding system,by fitting a power transmitting device in a road or an exterior wall,charging can be performed not only when the electric vehicle is stoppedbut also when driven. In addition, the contactless power feeding systemmay be utilized to perform transmission and reception of electric powerbetween vehicles. Furthermore, a solar cell may be provided in theexterior of the automobile to charge the storage battery when theautomobile stops or moves. To supply electric power in such acontactless manner, an electromagnetic induction method or a magneticresonance method can be used.

According to one embodiment of the present invention, the storagebattery can have improved cycle characteristics and reliability.Furthermore, according to one embodiment of the present invention, thestorage battery itself can be made more compact and lightweight as aresult of improved characteristics of the storage battery. The compactand lightweight storage battery contributes to a reduction in the weightof a vehicle, and thus increases the driving distance. Furthermore, thestorage battery included in the vehicle can be used as a power sourcefor supplying electric power to products other than the vehicle. In sucha case, the use of a commercial power source can be avoided at peak timeof electric power demand.

This embodiment can be implemented in combination with any of the otherembodiments as appropriate.

Embodiment 4

A battery management unit (BMU) that can be used in combination with thestorage batteries described in Embodiments 1 to 3 as battery cells andtransistors that are suitable for a circuit included in the batterymanagement unit will be described with reference to FIG. 17, FIGS. 18Ato 18C, FIG. 19, FIG. 20, FIGS. 21A to 21C, FIG. 22, and FIG. 23. Inthis embodiment, in particular, a battery management unit of a storagebattery including battery cells connected in series will be described.

When the plurality of battery cells connected in series are repeatedlycharged and discharged, there occur variations in charge and dischargecharacteristics among the battery cells, which causes variations incapacity (output voltage) among the battery cells. The dischargecapacity of all the plurality of battery cells connected in seriesdepends on the capacity of the battery cell that is low. The variationsin capacity among the battery cells reduce the discharge capacity of allthe battery cells. Furthermore, when charge is performed based on thecapacity of the battery cell that is low, the battery cells might beundercharged. In contrast, when charge is performed based on thecapacity of the battery cell that is high, the battery cells might beovercharged.

Thus, the battery management unit of the storage battery including thebattery cells connected in series has a function of reducing variationsin capacity among the battery cells, which cause an undercharge and anovercharge. Examples of a circuit configuration for reducing variationsin capacity among battery cells include a resistive type, a capacitivetype, and an inductive type, and a circuit configuration that can reducevariations in capacity among battery cells using transistors with a lowoff-state current will be explained here as an example.

A transistor including an oxide semiconductor in its channel formationregion (an OS transistor) is preferably used as the transistor with alow off-state current. When an OS transistor with a low off-statecurrent is used in the circuit of the battery management unit of thestorage battery, the amount of charge that leaks from a battery can bereduced, and reduction in capacity with the lapse of time can besuppressed.

As the oxide semiconductor used in the channel formation region, anIn-M-Zn oxide (M is Ga, Sn, Y, Zr, La, Ce, or Nd) is used. In the casewhere the atomic ratio of the metal elements of a target for forming anoxide semiconductor film is In:M:Zn=x₁:y₁:z₁, x₁/y₁ is preferablygreater than or equal to ⅓ and less than or equal to 6, more preferablygreater than or equal to 1 and less than or equal to 6, and z₁/y₁ ispreferably greater than or equal to ⅓ and less than or equal to 6, morepreferably greater than or equal to 1 and less than or equal to 6. Notethat when z₁/y₁ is greater than or equal to 1 and less than or equal to6, a CAAC-OS film as the oxide semiconductor film is easily formed.

Here, the details of the CAAC-OS film will be described.

A CAAC-OS film is one of oxide semiconductor films having a plurality ofc-axis aligned crystal parts.

In a combined analysis image (also referred to as a high-resolution TEMimage) of a bright-field image and a diffraction pattern of a CAAC-OSfilm, which is obtained using a transmission electron microscope (TEM),a plurality of crystal parts can be observed. However, in thehigh-resolution TEM image, a boundary between crystal parts, that is, agrain boundary is not clearly observed. Thus, in the CAAC-OS film, areduction in electron mobility due to the grain boundary is less likelyto occur.

According to the high-resolution cross-sectional TEM image of theCAAC-OS film observed in the direction substantially parallel to thesample surface, metal atoms are arranged in a layered manner in thecrystal parts. Each metal atom layer reflects unevenness of a surfaceover which the CAAC-OS film is formed (hereinafter, a surface over whichthe CAAC-OS film is formed is referred to as a formation surface) or thetop surface of the CAAC-OS film, and is arranged parallel to theformation surface or the top surface of the CAAC-OS film.

On the other hand, according to the plan high-resolution TEM image ofthe CAAC-OS film observed in the direction substantially perpendicularto the sample surface, metal atoms are arranged in a triangular orhexagonal arrangement in the crystal parts. However, there is noregularity of arrangement of metal atoms between different crystalparts.

For example, when the structure of a CAAC-OS including an InGaZnO₄crystal is analyzed by an out-of-plane method using an X-ray diffraction(XRD) apparatus, a peak may appear at a diffraction angle (2 θ) ofaround 31°. This peak is derived from the (009) plane of the InGaZnO₄crystal, which indicates that crystals in the CAAC-OS film have c-axisalignment, and that the c-axes are aligned in the directionsubstantially perpendicular to the formation surface or the top surfaceof the CAAC-OS film.

Note that in analysis of the CAAC-OS film by an out-of-plane method,another peak may appear when 2 θ is around 36°, in addition to the peakat 2 θ of around 31°. The peak at 2 θ of around 36° indicates that acrystal having no c-axis alignment is included in part of the CAAC-OSfilm. It is preferable that in the CAAC-OS film, a peak appear when 2 θis around 31° and that a peak not appear when 2 θ is around 36°.

The CAAC-OS film is an oxide semiconductor film with low impurityconcentration. The impurity is an element other than the main componentsof the oxide semiconductor film, such as hydrogen, carbon, silicon, or atransition metal element. In particular, an element (specifically,silicon or the like) having higher strength of bonding to oxygen than ametal element included in an oxide semiconductor film extracts oxygenfrom the oxide semiconductor film, which results in disorder of theatomic arrangement and reduced crystallinity of the oxide semiconductorfilm. Furthermore, a heavy metal such as iron or nickel, argon, carbondioxide, or the like has a large atomic radius (molecular radius), andthus disturbs the atomic arrangement of the oxide semiconductor film andcauses a decrease in crystallinity when it is contained in the oxidesemiconductor film. Note that the impurity contained in the oxidesemiconductor might serve as a carrier trap or a carrier generationsource.

The CAAC-OS film is an oxide semiconductor having a low density ofdefect states. In some cases, oxygen vacancies in the oxidesemiconductor film serve as carrier traps or serve as carrier generationsources when hydrogen is captured therein, for example.

The state in which impurity concentration is low and density of defectstates is low (the number of oxygen vacancies is small) is referred toas a “highly purified intrinsic” or “substantially intrinsic” state. Ahighly purified intrinsic or substantially intrinsic oxide semiconductorhas few carrier generation sources, and thus can have a low carrierdensity. Therefore, a transistor including the oxide semiconductor filmrarely has negative threshold voltage (is rarely normally on). Thehighly purified intrinsic or substantially intrinsic oxide semiconductorfilm has few carrier traps. Accordingly, the transistor including theoxide semiconductor film has little variation in electricalcharacteristics and high reliability. Charge trapped by the carriertraps in the oxide semiconductor film takes a long time to be releasedand might behave like fixed charge. Thus, the transistor including theoxide semiconductor film having high impurity concentration and a highdensity of defect states has unstable electrical characteristics in somecases.

With the use of the CAAC-OS film in a transistor, variation in theelectrical characteristics of the transistor due to irradiation withvisible light or ultraviolet light is small.

Since the OS transistor has a wider band gap than a transistor includingsilicon in its channel formation region (a Si transistor), dielectricbreakdown is unlikely to occur when a high voltage is applied. Althougha voltage of several hundreds of volts is generated when battery cellsare connected in series, the above-described OS transistor is suitablefor a circuit of a battery management unit which is used for suchbattery cells in the storage battery.

FIG. 17 is an example of a block diagram of the storage battery. Astorage battery BT00 illustrated in FIG. 17 includes a terminal pairBT01, a terminal pair BT02, a switching control circuit BT03, aswitching circuit BT04, a switching circuit BT05, a voltagetransformation control circuit BT06, a voltage transformer circuit BT07,and a battery portion BT08 including a plurality of battery cells BT09connected in series.

In the storage battery BT00 illustrated in FIG. 17, a portion includingthe terminal pair BT01, the terminal pair BT02, the switching controlcircuit BT03, the switching circuit BT04, the switching circuit BT05,the voltage transformation control circuit BT06, and the voltagetransformer circuit BT07 can be referred to as a battery managementunit.

The switching control circuit BT03 controls operations of the switchingcircuits BT04 and BT05. Specifically, the switching control circuit BT03selects battery cells to be discharged (a discharge battery cell group)and battery cells to be charged (a charge battery cell group) inaccordance with voltage measured for every battery cell BT09.

Furthermore, the switching control circuit BT03 outputs a control signalS1 and a control signal S2 on the basis of the selected dischargebattery cell group and the selected charge battery cell group. Thecontrol signal S1 is output to the switching circuit BT04. The controlsignal S1 controls the switching circuit BT04 so that the terminal pairBT01 and the discharge battery cell group are connected. In addition,the control signal S2 is output to the switching circuit BT05. Thecontrol signal S2 controls the switching circuit BT05 so that theterminal pair BT02 and the charge battery cell group are connected.

The switching control circuit BT03 generates the control signal S1 andthe control signal S2 on the basis of the connection relation of theswitching circuit BT04, the switching circuit BT05, and the voltagetransformer circuit BT07 so that terminals having the same polarity ofthe terminal pair BT01 and the discharge battery cell group areconnected with each other, or terminals having the same polarity of theterminal pair BT02 and the charge battery cell group are connected witheach other.

The operations of the switching control circuit BT03 will be describedin detail.

First, the switching control circuit BT03 measures the voltage of eachof the plurality of battery cells BT09. Then, the switching controlcircuit BT03 determines that the battery cell BT09 having a voltagehigher than a predetermined threshold value is a high-voltage batterycell (high-voltage cell) and that the battery cell BT09 having a voltagelower than the predetermined threshold value is a low-voltage batterycell (low-voltage cell), for example.

As a method to determine whether a battery cell is a high-voltage cellor a low-voltage cell, any of various methods can be employed. Forexample, the switching control circuit BT03 may determine whether eachbattery cell BT09 is a high-voltage cell or a low-voltage cell on thebasis of the voltage of the battery cell BT09 having the highest voltageor the lowest voltage among the plurality of battery cells BT09. In thiscase, the switching control circuit BT03 can determine whether eachbattery cell BT09 is a high-voltage cell or a low-voltage cell by, forexample, determining whether or not the ratio of the voltage of eachbattery cell BT09 to the reference voltage is the predetermined value ormore. Then, the switching control circuit BT03 determines a chargebattery cell group and a discharge battery cell group on the basis ofthe determination result.

Note that high-voltage cells and low-voltage cells are mixed in variousstates in the plurality of battery cells BT09. For example, theswitching control circuit BT03 selects a portion having the largestnumber of high-voltage cells connected in series as the dischargebattery cell group of mixed high-voltage cells and low-voltage cells.Furthermore, the switching control circuit BT03 selects a portion havingthe largest number of low-voltage cells connected in series as thecharge battery cell group. In addition, the switching control circuitBT03 may preferentially select the battery cells BT09 which are almostovercharged or over-discharged as the discharge battery cell group orthe charge battery cell group.

Here, operation examples of the switching control circuit BT03 in thisembodiment will be described with reference to FIGS. 18A to 18C. FIGS.18A to 18C illustrate the operation examples of the switching controlcircuit BT03. Note that FIGS. 18A to 18C each illustrate the case wherefour battery cells BT09 are connected in series as an example forconvenience of explanation.

FIG. 18A shows the case where the relation of voltages Va, Vb, Vc, andVd is Va=Vb=Vc>Vd where the voltages Va, Vb, Vc, and Vd are the voltagesof a battery cell a, a battery cell b, a battery cell c, and a batterycell d, respectively. That is, a series of three high-voltage cells a toc and one low-voltage cell d are connected in series. In this case, theswitching control circuit BT03 selects the series of three high-voltagecells a to c as the discharge battery cell group. In addition, theswitching control circuit BT03 selects the low-voltage cell d as thecharge battery cell group.

Next, FIG. 18B shows the case where the relation of the voltages isVc>Va=Vb>>Vd. That is, a series of two low-voltage cells a and b, onehigh-voltage cell c, and one low-voltage cell d which is almostover-discharged are connected in series. In this case, the switchingcontrol circuit BT03 selects the high-voltage cell c as the dischargebattery cell group. Since the low-voltage cell d is almostover-discharged, the switching control circuit BT03 preferentiallyselects the low-voltage cell d as the charge battery cell group insteadof the series of two low-voltage cells a and b.

Lastly, FIG. 18C shows the case where the relation of the voltages isVa>Vb=Vc=Vd. That is, one high-voltage cell a and a series of threelow-voltage cells b to d are connected in series. In this case, theswitching control circuit BT03 selects the high-voltage cell a as thedischarge battery cell group. In addition, the switching control circuitBT03 selects the series of three low-voltage cells b to d as the chargebattery cell group.

On the basis of the determination result shown in the examples of FIGS.18A to 18C, the switching control circuit BT03 outputs the controlsignal S1 and the control signal S2 to the switching circuit BT04 andthe switching circuit BT05, respectively. Information showing thedischarge battery cell group, which is the connection destination of theswitching circuit BT04, is set in the control signal S1. Informationshowing the charge battery cell group, which is the connectiondestination of the switching circuit BT05 is set in the control signalS2.

The above is the detailed description of the operations of the switchingcontrol circuit BT03.

The switching circuit BT04 sets the connection destination of theterminal pair BT01 at the discharge battery cell group selected by theswitching control circuit BT03, in response to the control signal S1output from the switching control circuit BT03.

The terminal pair BT01 includes a pair of terminals A1 and A2. Theswitching circuit BT04 connects one of the pair of terminals A1 and A2to a positive electrode terminal of the battery cell BT09 positioned onthe most upstream side (on the high potential side) of the dischargebattery cell group, and the other to a negative electrode terminal ofthe battery cell BT09 positioned on the most downstream side (on the lowpotential side) of the discharge battery cell group. Note that theswitching circuit BT04 can recognize the position of the dischargebattery cell group on the basis of the information set in the controlsignal S1.

The switching circuit BT05 sets the connection destination of theterminal pair BT02 at the charge battery cell group selected by theswitching control circuit BT03, in response to the control signal S2output from the switching control circuit BT03.

The terminal pair BT02 includes a pair of terminals B1 and B2. Theswitching circuit BT05 sets the connection destination of the terminalpair BT02 by connecting one of the pair of terminals B1 and B2 to apositive electrode terminal of the battery cell BT09 positioned on themost upstream side (on the high potential side) of the charge batterycell group, and the other to a negative electrode terminal of thebattery cell BT09 positioned on the most downstream side (on the lowpotential side) of the charge battery cell group. Note that theswitching circuit BT05 can recognize the position of the charge batterycell group on the basis of the information set in the control signal S2.

FIG. 19 and FIG. 20 are circuit diagrams showing configuration examplesof the switching circuits BT04 and BT05.

In FIG. 19, the switching circuit BT04 includes a plurality oftransistors BT10, a bus BT11, and a bus BT12. The bus BT11 is connectedto the terminal A1. The bus BT12 is connected to the terminal A2.Sources or drains of the plurality of transistors BT10 are connectedalternately to the bus BT11 and the bus BT12. The sources or drainswhich are not connected to the bus BT11 and the bus BT12 of theplurality of transistors BT10 are each connected between two adjacentbattery cells BT09.

The source or drain of the transistor BT10 which is not connected to thebus BT12 on the most upstream side of the plurality of transistors BT10is connected to the positive electrode terminal of the battery cell BT09on the most upstream side of the battery portion BT08. The source ordrain of the transistor BT10 which is not connected to the bus BT12 ofthe transistor BT10 on the most downstream side of the plurality oftransistors BT10 is connected to the negative electrode terminal of thebattery cell BT09 on the most downstream side of the battery portionBT08.

The switching circuit BT04 connects the discharge battery cell group tothe terminal pair BT01 by bringing one of the plurality of transistorsBT10 which are connected to the bus BT11 and one of the plurality oftransistors BT10 which are connected to the bus BT12 into an on state inresponse to the control signal S1 supplied to gates of the plurality oftransistors BT10. Accordingly, the positive electrode terminal of thebattery cell BT09 on the most upstream side of the discharge batterycell group is connected to one of the pair of terminals A1 and A2. Inaddition, the negative electrode terminal of the battery cell BT09 onthe most downstream side of the discharge battery cell group isconnected to the other of the pair of terminals A1 and A2 (i.e., aterminal which is not connected to the positive electrode terminal).

An OS transistor is preferably used as the transistor BT10. Since theoff-state current of the OS transistor is low, the amount of charge thatleaks from the battery cell which does not belong to the dischargebattery cell group can be reduced, and reduction in capacity with thelapse of time can be suppressed. In addition, dielectric breakdown isunlikely to occur in the OS transistor when a high voltage is applied.Therefore, the battery cell BT09 and the terminal pair BT01, which areconnected to the transistor BT10 in an off state, can be insulated fromeach other even when the output voltage of the discharge battery cellgroup is high.

In FIG. 19, the switching circuit BT05 includes a plurality oftransistors BT13, a current control switch BT14, a bus BT15, and a busBT16. The bus BT15 and the bus BT16 are provided between the pluralityof transistors BT13 and the current control switch BT14. Sources ordrains of the plurality of transistors BT13 are connected alternately tothe bus BT15 and the bus BT16. The sources or drains which are notconnected to the bus BT15 and the bus BT16 of the plurality oftransistors BT13 are each connected between two adjacent battery cellsBT09.

The source or drain of the transistor BT13 which is not connected to thebus BT16 on the most upstream side of the plurality of transistors BT13is connected to the positive electrode terminal of the battery cell BT09on the most upstream side of the battery portion BT08. The source or adrain of the transistor BT13 which is not connected to the bus BT16 onthe most downstream side of the plurality of transistors BT13 isconnected to the negative electrode terminal of the battery cell BT09 onthe most downstream side of the battery portion BT08.

An OS transistor is preferably used as the transistors BT13 like thetransistors BT10. Since the off-state current of the OS transistor islow, the amount of charge that leaks from the battery cells which do notbelong to the charge battery cell group can be reduced, and reduction incapacity with the lapse of time can be suppressed. In addition,dielectric breakdown is unlikely to occur in the OS transistor when ahigh voltage is applied. Therefore, the battery cell BT09 and theterminal pair BT02, which are connected to the transistor BT13 in an offstate, can be insulated from each other even when a voltage for chargingthe charge battery cell group is high.

The current control switch BT14 includes a switch pair BT17 and a switchpair BT18. Terminals on one end of the switch pair BT17 are connected tothe terminal B1. Terminals on the other end of the switch pair BT17extend from two switches. One switch is connected to the bus BT15, andthe other switch is connected to the bus BT16. Terminals on one end ofthe switch pair BT18 are connected to the terminal B2. Terminals on theother end of the switch pair BT18 extend from two switches. One switchis connected to the bus BT15, and the other switch is connected to thebus BT16.

OS transistors are preferably used for the switches included in theswitch pair BT17 and the switch pair BT18 like the transistors BT10 andBT13.

The switching circuit BT05 connects the charge battery cell group andthe terminal pair BT02 by controlling the combination of on and offstates of the transistors BT13 and the current control switch BT14 inresponse to the control signal S2.

For example, the switching circuit BT05 connects the charge battery cellgroup and the terminal pair BT02 in the following manner.

The switching circuit BT05 brings a transistor BT13 connected to thepositive electrode terminal of the battery cell BT09 on the mostupstream side of the charge battery cell group into an on state inresponse to the control signal S2 supplied to gates of the plurality oftransistors BT13. In addition, the switching circuit BT05 brings atransistor BT13 connected to the negative electrode terminal of thebattery cell BT09 on the most downstream side of the charge battery cellgroup into an on state in response to the control signal S2 supplied tothe gates of the plurality of transistors BT13.

The polarities of voltages applied to the terminal pair BT02 can vary inaccordance with the configurations of the voltage transformer circuitBT07 and the discharge battery cell group connected to the terminal pairBT01. In order to supply a current in the direction for charging thecharge battery cell group, terminals with the same polarity of theterminal pair BT02 and the charge battery cell group are required to beconnected to each other. In view of this, the current control switchBT14 is controlled by the control signal S2 so that the connectiondestination of the switch pair BT17 and that of the switch pair BT18 arechanged in accordance with the polarities of the voltages applied to theterminal pair BT02.

The state where voltages are applied to the terminal pair BT02 so as tomake the terminal B1 a positive electrode and the terminal B2 a negativeelectrode will be described as an example. Here, in the case where thebattery cell BT09 positioned on the most downstream side of the batteryportion BT08 is in the charge battery cell group, the switch pair BT17is controlled to be connected to the positive electrode terminal of thebattery cell BT09 in response to the control signal S2. That is, theswitch of the switch pair BT17 connected to the bus BT16 is turned on,and the switch of the switch pair BT17 connected to the bus BT15 isturned off. In contrast, the switch pair BT18 is controlled to beconnected to the negative electrode terminal of the battery cell BT09positioned on the most downstream side of the battery portion BT08 inresponse to the control signal S2. That is, the switch of the switchpair BT18 connected to the bus BT15 is turned on, and the switch of theswitch pair BT18 connected to the bus BT16 is turned off. In thismanner, terminals with the same polarity of the terminal pair BT02 andthe charge battery cell group are connected to each other. In addition,the current which flows from the terminal pair BT02 is controlled to besupplied in a direction so as to charge the charge battery cell group.

In addition, instead of the switching circuit BT05, the switchingcircuit BT04 may include the current control switch BT14. In that case,the polarities of the voltages applied to the terminal pair BT02 arecontrolled by controlling the polarities of the voltages applied to theterminal pair BT01 in response to the operation of the current controlswitch BT14 and the control signal S1. Thus, the current control switchBT14 controls the direction of current which flows to the charge batterycell group from the terminal pair BT02.

FIG. 20 is a circuit diagram illustrating configuration examples of theswitching circuit BT04 and the switching circuit BT05 which aredifferent from those of FIG. 19.

In FIG. 20, the switching circuit BT04 includes a plurality oftransistor pairs BT21, a bus BT24, and a bus BT25. The bus BT24 isconnected to the terminal A1. The bus BT25 is connected to the terminalA2. Terminals on one end of each of the plurality of transistor pairsBT21 extend from a transistor BT22 and a transistor BT23. Sources ordrains of the transistors BT22 are connected to the bus BT24. Sources ordrains of the transistors BT23 are connected to the bus BT25. Inaddition, terminals on the other end of each of the plurality oftransistor pairs are connected between two adjacent battery cells BT09.The terminals on the other end of the transistor pair BT21 on the mostupstream side of the plurality of transistor pairs BT21 are connected tothe positive electrode terminal of the battery cell BT09 on the mostupstream side of the battery portion BT08. The terminals on the otherend of the transistor pair BT21 on the most downstream side of theplurality of transistor pairs BT21 are connected to a negative electrodeterminal of the battery cell BT09 on the most downstream side of thebattery portion BT08.

The switching circuit BT04 switches the connection destination of thetransistor pair BT21 to one of the terminal A1 and the terminal A2 byturning on or off the transistors BT22 and BT23 in response to thecontrol signal S1. Specifically, when the transistor BT22 is turned on,the transistor BT23 is turned off, so that the connection destination ofthe transistor pair BT21 is the terminal A1. On the other hand, when thetransistor BT23 is turned on, the transistor BT22 is turned off, so thatthe connection destination of the transistor pair BT21 is the terminalA2. Which of the transistors BT22 and BT23 is turned on is determined bythe control signal S1.

Two transistor pairs BT21 are used to connect the terminal pair BT01 andthe discharge battery cell group. Specifically, the connectiondestinations of the two transistor pairs BT21 are determined on thebasis of the control signal S1, and the discharge battery cell group andthe terminal pair BT01 are connected. The connection destinations of thetwo transistor pairs BT21 are controlled by the control signal S1 sothat one of the connection destinations is the terminal A1 and the otheris the terminal A2.

The switching circuit BT05 includes a plurality of transistor pairsBT31, a bus BT34, and a bus BT35. The bus BT34 is connected to theterminal B1. The bus BT35 is connected to the terminal B2. Terminals onone end of each of the plurality of transistor pairs BT31 extend from atransistor BT32 and a transistor BT33. The terminal on one end extendingfrom the transistor BT32 is connected to the bus BT34. The terminal onone end extending from the transistor BT33 is connected to the bus BT35.Terminals on the other end of each of the plurality of transistor pairsBT31 are connected between two adjacent battery cells BT09. The terminalon the other end of the transistor pair BT31 on the most upstream sideof the plurality of transistor pairs BT31 is connected to the positiveelectrode terminal of the battery cell BT09 on the most upstream side ofthe battery portion BT08. The terminal on the other end of thetransistor pair BT31 on the most downstream side of the plurality oftransistor pairs BT31 is connected to the negative electrode terminal ofthe battery cell BT09 on the most downstream side of the battery portionBT08.

The switching circuit BT05 switches the connection destination of thetransistor pair BT31 to one of the terminal B1 and the terminal B2 byturning on or off the transistors BT32 and BT33 in response to thecontrol signal S2. Specifically, when the transistor BT32 is turned on,the transistor BT33 is turned off, so that the connection destination ofthe transistor pair BT31 is the terminal B1. On the other hand, when thetransistor BT33 is turned on, the transistor BT32 is turned off, so thatthe connection destination of the transistor pair BT31 is the terminalB2. Which of the transistors BT32 and BT33 is turned on is determined bythe control signal S2.

Two transistor pairs BT31 are used to connect the terminal pair BT02 andthe charge battery cell group. Specifically, the connection destinationsof the two transistor pairs BT31 are determined on the basis of thecontrol signal S2, and the charge battery cell group and the terminalpair BT02 are connected. The connection destinations of the twotransistor pairs BT31 are controlled by the control signal S2 so thatone of the connection destinations is the terminal B1 and the other isthe terminal B2.

The connection destinations of the two transistor pairs BT31 aredetermined by the polarities of the voltages applied to the terminalpair BT02. Specifically, in the case where voltages which make theterminal B1 a positive electrode and the terminal B2 a negativeelectrode are applied to the terminal pair BT02, the transistor pairBT31 on the upstream side is controlled by the control signal S2 so thatthe transistor BT32 is turned on and the transistor BT33 is turned off.In contrast, the transistor pair BT31 on the downstream side iscontrolled by the control signal S2 so that the transistor BT33 isturned on and the transistor BT32 is turned off. In the case wherevoltages which make the terminal B1 a negative electrode and theterminal B2 a positive electrode are applied to the terminal pair BT02,the transistor pair BT31 on the upstream side is controlled by thecontrol signal S2 so that the transistor BT33 is turned on and thetransistor BT32 is turned off. In contrast, the transistor pair BT31 onthe downstream side is controlled by the control signal S2 so that thetransistor BT32 is turned on and the transistor BT33 is turned off. Inthis manner, terminals with the same polarity of the terminal pair BT02and the charge battery cell group are connected to each other. Inaddition, the current which flows from the terminal pair BT02 iscontrolled to be supplied in the direction for charging the chargebattery cell group.

The voltage transformation control circuit BT06 controls the operationof the voltage transformer circuit BT07. The voltage transformationcontrol circuit BT06 generates a voltage transformation signal S3 forcontrolling the operation of the voltage transformer circuit RT07 on thebasis of the number of the battery cells RT09 included in the dischargebattery cell group and the number of the battery cells BT09 included inthe charge battery cell group and outputs the voltage transformationsignal S3 to the voltage transformer circuit BT07.

In the case where the number of the battery cells BT09 included in thedischarge battery cell group is larger than that included in the chargebattery cell group, it is necessary to prevent a charging voltage whichis too high from being applied to the charge battery cell group. Thus,the voltage transformation control circuit BT06 outputs the voltagetransformation signal S3 for controlling the voltage transformer circuitBT07 so that a discharging voltage (Vdis) is lowered within a rangewhere the charge battery cell group can be charged.

In the case where the number of the battery cells BT09 included in thedischarge battery cell group is less than or equal to that included inthe charge battery cell group, a charging voltage necessary for chargingthe charge battery cell group needs to be ensured. Therefore, thevoltage transformation control circuit BT06 outputs the voltagetransformation signal S3 for controlling the voltage transformer circuitBT07 so that the discharging voltage (Vdis) is raised within a rangewhere a charging voltage which is too high is not applied to the chargebattery cell group.

The voltage value of the charging voltage which is too high isdetermined in the light of product specifications and the like of thebattery cell BT09 used in the battery portion BT08. The voltage which israised or lowered by the voltage transformer circuit BT07 is applied asa charging voltage (Vcha) to the terminal pair BT02.

Here, operation examples of the voltage transformation control circuitBT06 in this embodiment will be described with reference to FIGS. 21A to21C. FIGS. 21A to 21C are conceptual diagrams for explaining theoperation examples of the voltage transformation control circuit BT06corresponding to the discharge battery cell group and the charge batterycell group described in FIGS. 18A to 18C. FIGS. 21A to 21C eachillustrate a battery control unit BT41. The battery control unit BT41includes the terminal pair BT01, the terminal pair BT02, the switchingcontrol circuit BT03, the switching circuit BT04, the switching circuitBT05, the voltage transformation control circuit BT06, and the voltagetransformer circuit BT07.

In an example illustrated in FIG. 21A, the series of three high-voltagecells a to c and one low-voltage cell d are connected in series asdescribed in FIG. 18A. In this case, as described using FIG. 18A, theswitching control circuit BT03 selects the high-voltage cells a to c asthe discharge battery cell group, and selects the low-voltage cell d asthe charge battery cell group. The voltage transformation controlcircuit BT06 calculates a conversion ratio N for converting thedischarging voltage (Vdis) into the charging voltage (Vcha) based on theratio of the number of the battery cells BT09 included in the chargebattery cell group to the number of the battery cells BT09 included inthe discharge battery cell group.

In the case where the number of the battery cells BT09 included in thedischarge battery cell group is larger than that included in the chargebattery cell group, when a discharging voltage is applied to theterminal pair BT02 without transforming the voltage, an overvoltage maybe applied to the battery cells BT09 included in the charge battery cellgroup through the terminal pair BT02. Thus, in the case of FIG. 21A, itis necessary that a charging voltage (Vcha) applied to the terminal pairBT02 be lower than the discharging voltage. In addition, in order tocharge the charge battery cell group, it is necessary that the chargingvoltage be higher than the total voltage of the battery cells BT09included in the charge battery cell group. Thus, the voltagetransformation control circuit BT06 sets the conversion ratio N largerthan the ratio of the number of the battery cells BT09 included in thecharge battery cell group to the number of the battery cells BT09included in the discharge battery cell group.

Thus, the voltage transformation control circuit BT06 preferably setsthe conversion ratio N larger than the ratio of the number of thebattery cells BT09 included in the charge battery cell group to thenumber of the battery cells BT09 included in the discharge battery cellgroup by about 1% to 10%. Here, the charging voltage is made higher thanthe voltage of the charge battery cell group, but the charging voltageis equal to the voltage of the charge battery cell group in reality.Note that the voltage transformation control circuit BT06 feeds acurrent for charging the charge battery cell group in accordance withthe conversion ratio N in order to make the voltage of the chargebattery cell group equal to the charging voltage. The value of thecurrent is set by the voltage transformation control circuit BT06.

In the example illustrated in FIG. 21A, since the number of the batterycells BT09 included in the discharge battery cell group is three and thenumber of the battery cells BT09 included in the charge battery cellgroup is one, the voltage transformation control circuit BT06 calculatesa value which is slightly larger than ⅓ as the conversion ratio N. Then,the voltage transformation control circuit BT06 outputs the voltagetransformation signal S3, which lowers the discharging voltage inaccordance with the conversion ratio N and converts the voltage into acharging voltage, to the voltage transformer circuit BT07. The voltagetransformer circuit BT07 applies the charging voltage which is obtainedby transformation in response to the voltage transformation signal S3 tothe terminal pair BTG2. Then, the battery cells BT09 included in thecharge battery cell group are charged with the charging voltage appliedto the terminal pair BT02.

In each of examples illustrated in FIGS. 21B and 21C, the conversionratio N is calculated in a manner similar to that of FIG. 21A. In eachof the examples illustrated in FIGS. 21B and 21C, since the number ofthe battery cells BT09 included in the discharge battery cell group isless than or equal to the number of the battery cells BT09 included inthe charge battery cell group, the conversion ratio N is 1 or more.Therefore, in this case, the voltage transformation control circuit BT06outputs the voltage transformation signal S3 for raising the dischargingvoltage and converting the voltage into the charging voltage.

The voltage transformer circuit BT07 converts the discharging voltageapplied to the terminal pair BT01 into a charging voltage in response tothe voltage transformation signal S3. The voltage transformer circuitBT07 applies the charging voltage to the terminal pair BT02. Here, thevoltage transformer circuit BT07 electrically insulates the terminalpair BT01 from the terminal pair BT02. Accordingly, the voltagetransformer circuit BT07 prevents a short circuit due to a differencebetween the absolute voltage of the negative electrode terminal of thebattery cell BT09 on the most downstream side of the discharge batterycell group and the absolute voltage of the negative electrode terminalof the battery cell BT09 on the most downstream side of the chargebattery cell group. Furthermore, the voltage transformer circuit BT07converts the discharging voltage, which is the total voltage of thedischarge battery cell group, into the charging voltage in response tothe voltage transformation signal S3 as described above.

An insulated direct current (DC)-DC converter or the like can be used inthe voltage transformer circuit BT07. In that case, the voltagetransformation control circuit BT06 controls the charging voltageconverted by the voltage transformer circuit BT07 by outputting a signalfor controlling the on/off ratio (the duty ratio) of the insulated DC-DCconverter as the voltage transformation signal S3.

Examples of the insulated DC-DC converter include a flyback converter, aforward converter, a ringing choke converter (RCC), a push-pullconverter, a half-bridge converter, and a full-bridge converter, and asuitable converter is selected in accordance with the value of theintended output voltage.

The configuration of the voltage transformer circuit BT07 including theinsulated DC-DC converter is illustrated in FIG. 22. An insulated DC-DCconverter BT51 includes a switch portion BT52 and a transformer BT53.The switch portion BT52 is a switch for switching on/off of theinsulated DC-DC converter, and a metal oxide semiconductor field-effecttransistor (MOSFET), a bipolar transistor, or the like is used as theswitch portion BT52. The switch portion BT52 periodically turns on andoff the insulated DC-DC converter BT51 in response to the voltagetransformation signal S3 for controlling the on/off ratio which isoutput from the voltage transformation control circuit BT06. The switchportion BT52 can have any of various structures in accordance with thetype of the insulated DC-DC converter which is used. The transformerBT53 converts the discharging voltage applied from the terminal pairBT01 into the charging voltage. In detail, the transformer BT53 operatesin conjunction with the on/off state of the switch portion BT52 andconverts the discharging voltage into the charging voltage in accordancewith the on-off ratio. As the time during which the switch portion BT52is on becomes longer in its switching period, the charging voltage isincreased. On the other hand, as the time during which the switchportion BT52 is on becomes shorter in its switching period, the chargingvoltage is decreased. In the case where the insulated DC-DC converter isused, the terminal pair BT01 and the terminal pair BT02 can be insulatedfrom each other inside the transformer BT53.

A flow of operations of the storage battery BT00 in this embodiment willbe described with reference to FIG. 23. FIG. 23 is a flow chart showingthe flow of the operations of the storage battery BT00.

First, the storage battery BT00 obtains a voltage measured for each ofthe plurality of battery cells B109 (step S001). Then, the storagebattery BT00 determines whether or not the condition for starting theoperation of reducing variations in voltage of the plurality of batterycells BT09 is satisfied (step S002). An example of the condition can bethat the difference between the maximum value and the minimum value ofthe voltage measured for each of the plurality of battery cells BT09 ishigher than or equal to the predetermined threshold value. In the casewhere the condition is not satisfied (step S002: NO), the storagebattery BT00 does not perform the following operation because voltagesof the battery cells BT09 are well balanced. In contrast, in the casewhere the condition is satisfied (step S002: YES), the storage batteryBT00 performs the operation of reducing variations in the voltage of thebattery cells BT09. In this operation, the storage battery BT00determines whether each battery cell BT09 is a high voltage cell or alow voltage cell on the basis of the measured voltage of each cell (stepS003). Then, the storage battery BT00 determines a discharge batterycell group and a charge battery cell group on the basis of thedetermination result (step S004). In addition, the storage battery BT00generates the control signal S1 for setting the connection destinationof the terminal pair BT01 to the determined discharge battery cellgroup, and the control signal S2 for setting the connection destinationof the terminal pair BT02 to the determined charge battery cell group(step S005). The storage battery BT00 outputs the generated controlsignals S1 and S2 to the switching circuit BT04 and the switchingcircuit BT05, respectively. Then, the switching circuit BT04 connectsthe terminal pair BT01 and the discharge battery cell group, and theswitching circuit BT05 connects the terminal pair BT02 and the dischargebattery cell group (step S006). The storage battery BT00 generates thevoltage transformation signal S3 based on the number of the batterycells BT09 included in the discharge battery cell group and the numberof the battery cells BT09 included in the charge battery cell group(step S007). Then, the storage battery BT00 converts, in response to thevoltage transformation signal S3, the discharging voltage applied to theterminal pair BT01 into a charging voltage and applies the chargingvoltage to the terminal pair BT02 (step S008). In this way, charge ofthe discharge battery cell group is transferred to the charge batterycell group.

Although the plurality of steps are shown in order in the flow chart ofFIG. 23, the order of performing the steps is not limited to the order.

According to the above embodiment, when charge is transferred from thedischarge battery cell group to the charge battery cell group, astructure where charge from the discharge battery cell group istemporarily stored, and the stored charge is sent to the charge batterycell group is unnecessary, unlike in the a capacitive type circuit.Accordingly, the charge transfer efficiency per unit time can beincreased. In addition, the switching circuit BT04 and the switchingcircuit BT05 determine which battery cell in the discharge battery cellgroup and the charge battery cell group to be connected to the voltagetransformer circuit.

Furthermore, the voltage transformer circuit BT07 converts thedischarging voltage applied to the terminal pair BT01 into the chargingvoltage based on the number of the battery cells BT09 included in thedischarge battery cell group and the number of the battery cells BT09included in the charge battery cell group, and applies the chargingvoltage to the terminal pair BT02. Thus, charge can be transferredwithout any problems regardless of how the battery cells BT09 areselected as the discharge battery cell group and the charge battery cellgroup.

Furthermore, the use of OS transistors as the transistor BT10 and thetransistor BT13 can reduce the amount of charge that leaks from thebattery cells BT09 not belonging to the charge battery cell group or thedischarge battery cell group. Accordingly, a decrease in capacity of thebattery cells BT09 which do not contribute to charging or dischargingcan be suppressed. In addition, the variations in characteristics of theOS transistor due to heat are smaller than those of an Si transistor.Accordingly, even when the temperature of the battery cells BT09 isincreased, an operation such as turning on or off the transistors inresponse to the control signals S1 and S2 can be performed normally.

This embodiment can be implemented in combination with any of the otherembodiments as appropriate.

This application is based on Japanese Patent Application serial no.2014-239736 filed with Japan Patent Office on Nov. 27, 2014, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A storage battery comprising: a positiveelectrode; a negative electrode; a separator between the positiveelectrode and the negative electrode; an exterior body surrounding thepositive electrode, the negative electrode, and the separator; a wiringprovided along the exterior body; and a circuit configured to detectdamage to the wiring, wherein one terminal of the wiring is electricallyconnected to the positive electrode, and wherein the other terminal ofthe wiring is electrically connected to the positive electrode throughthe circuit.
 2. A storage battery comprising: a positive electrode; anegative electrode a tab electrode; a wiring; a separator between thepositive electrode and the negative electrode; an exterior bodysurrounding the positive electrode, the negative electrode, and theseparator; and a circuit configured to detect damage to the wiring,wherein the tab electrode is connected to one of the positive electrodeand the negative electrode, wherein the wiring is provided along the tabelectrode, wherein one terminal of the wiring is electrically connectedto the positive electrode, and wherein the other terminal of the wiringis electrically connected to the positive electrode.